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PlatinumMetalsReview

www.platinummetalsreview.comE-ISSN 1471–0676

VOLUME 52 NUMBER 1 JANUARY 2008

E-ISSN 1471–0676

PLATINUM METALS REVIEWA Quarterly Survey of Research on the Platinum Metals and

of Developments in their Application in Industrywww.platinummetalsreview.com

VOL. 52 JANUARY 2008 NO. 1

Contents

Metal-Ligand Exchange Kinetics in Platinum 2and Ruthenium Complexes

By Jan Reedijk

The Tenth Grove Fuel Cell Symposium 12A conference review by Donald S. Cameron

“Medicinal Applications of Coordination Chemistry” 21A book review by Peter J. Sadler

Diesel Engine Emissions and Their Control 23By Tim Johnson

Palladium Catalysed C–C Coupling: Then and Now 38By Chris Barnard

“Frontiers in Transition Metal-Containing Polymers” 46A book review by Kaushik Mallick

Building a Thermodynamic Database for 48Platinum-Based Superalloys: Part III

By J. Preußner, S. N. Prins, M. Wenderoth, R. Völkl and U. Glatzel

“Adventures at the Bench” 52A book review by Christopher Corti

“Platinum 2007 Interim Review” 54

Abstracts 56

New Patents 59

Final Analysis: Particle Size Analysis of 61Supported Platinum Catalysts by TEM

By D. Ozkaya

Communications should be addressed to: The Editor, Barry W. Copping, Platinum Metals Review, [email protected]; Johnson Matthey Public Limited Company, Orchard Road, Royston, Hertfordshire SG8 5HE, U.K.

2

Since the appearance of the early review on cis-diamminedichloridoplatinum(II), commonly knownas cisplatin, 1, in this Journal (1), and its early success-es in the treatment of a variety of tumours, the topicsof metal-DNA binding and platinum antitumourchemistry have attracted considerable interest fromchemists, pharmacologists, biochemists, biologistsand medical researchers (2). In fact cisplatin and thelater compounds carboplatin, 2, and oxaliplatin, 3,enjoy the status of the world’s best-selling anticancerdrugs. This interest has stimulated much interdis-ciplinary scientific activity, which has already yieldedquite detailed understanding of the mechanism of

action of cisplatin and related drugs. This knowledgehas clearly resulted in much improved clinicaladministration protocols, as well as motivatedresearch on other, related drugs containing transitionmetals, and their applications.

All chemotherapeutic drugs have drawbacks,including intrinsic or acquired resistance, toxicity,and consequent side effects. Cisplatin is no excep-tion. Efforts to mitigate the drawbacks haveprompted chemists to synthesise a variety of ana-logues, but only a handful of new drugs haveresulted that have been shown to be suitable for clinical application. Improved understanding of themechanism of action of cisplatin, resulting from theefforts of many research groups during the last twodecades, has rationalised the design of new platinumdrugs, and drugs based on other metals such asruthenium (3–7). Nevertheless, many mechanisticquestions remain, especially for the drugs containingmetals other than platinum, and for the most recentderivatives of cisplatin (2, 8, 9).

Platinum Metals Rev., 2008, 52, (1), 2–11

Metal-Ligand Exchange Kinetics inPlatinum and Ruthenium ComplexesSIGNIFICANCE FOR EFFECTIVENESS AS ANTICANCER DRUGS

By Jan ReedijkLeiden Institute of Chemistry, PO Box 9502, 2300 RA, Leiden, The Netherlands; E-mail: [email protected]

Metal coordination compounds with ‘slow’metal-ligand exchange rates, comparable to thoseof cell division processes, often appear to be highly active in killing cancer cell lines. This isparticularly marked in platinum and ruthenium complexes. Classical examples such as cisplatin,as well as very recent examples from the author’s and other work, will be discussed in detail,and in the context of the current knowledge of the mechanism of antitumour action. It is shownthat even though much is known about the molecular mechanism of action of cisplatin,many challenging questions are left for future research. For the ruthenium anticancer drugsmolecular mechanistic studies are only at the beginning. Mechanistic studies on both platinumand ruthenium compounds have, however, opened many new avenues of research that maylead to the design of completely new drugs.

DOI: 10.1595/147106708X255987

ClCl

NH3Pt

NH3

1 Cisplatin

O

OO

O

NH3

NH3Pt

2 Carboplatin

O

O

NH2

NH2

PtO

O

3 Oxaliplatin

This overview will begin with a brief introductionto the molecular, kinetic and thermodynamic detailsof the coordination chemistry of medicinally relevantmetals, focusing on platinum, ruthenium and othernoble metals that have been shown to possessimportant biological properties. The metal–ligandcoordination bond appears to be particularly signifi-cant here. The bond is usually four to eight timesweaker than a covalent bond, and there are largevariations in ligand exchange kinetics for differentmetal-ligand pairs. This aspect will be introducedfirst, and will recur in later parts of the overview.

The central part of the overview will briefly sum-marise the state of the art in metal anticancer drugsand the current mechanistic insights, not only for cis-platin and related platinum drugs, but also fornon-platinum drugs and candidate drugs.

Finally, an account will be given of the design,synthesis, structure and biological activities of newbifunctional and multifunctional platinum, rutheni-um and mixed-platinum group metal (pgm)compounds with bridging ligands, and their possibledevelopment as anticancer drugs, or for other appli-cations.

Ligand Exchange Kinetics inCoordination Compounds

To address such issues as structure, reactivity and(in)stability in the chemistry of metal coordinationcompounds, detailed knowledge of their thermo-dynamics and kinetics is important, in addition toproper knowledge of the geometric and electronicstructures of the compounds.

Most chemists and many other scientists are fullyconversant with classical covalent chemical bonds,such as C–H, C–C, O–H and N–H. These singlebonds usually have a strength of some 250 to 500 kJ mol–1 (in older units: 60 to 120 kcal mol–1)(10). Double bonds as in C=O and C=N, and triplebonds as in dinitrogen (N≡N), have strengths up to500 and 800 kJ mol–1 respectively.

In addition to these covalent bonds, a large classof so-called non-covalent bonds is known. Here,much weaker interactions are found, the bonds areusually easily formed and broken, and so-calledsupramolecular structures may be generated.Examples of such bonds are:

(a) Coordination bonds (50 to 150 kJ mol–1)(b) Hydrogen bonds (20 to 60 kJ mol–1)(c) Stacking of aromatic ring systems (10 to 40

kJ mol–1)(d) Metal–metal bonds (50 to 150 kJ mol–1)(e) Other hydrophobic interactions (below 50

kJ mol–1)(f) Ionic bonds, as in lattices such as NaCl, where

each Na+ ion is surrounded by six chloride ions;these bonds dissociate upon dissolution in waterand may be compared in strength with coord-ination bonds.Even though the bond strength values above are

merely indicative of an order of magnitude, theyclearly indicate that such bonds are weaker than clas-sical covalent bonds. These weak interactions play animportant role, for instance in protein structures(whether secondary, tertiary or quaternary), and inDNA structures (stacks within the helix, doublehelices). Many such bonds acting in concert, as inWatson-Crick base pairing, or over the range of sev-eral stacks along the DNA helix, may generate arather strong interaction and hence a high thermo-dynamic stability.

In addition to the thermodynamic stability ofmolecules and aggregates, their kinetic stability mustbe considered. This parameter is far less discussed inthe literature, and it was the late Professor HenryTaube (Nobel Prize in Chemistry, 1983), who devel-oped this field (11). He explained why some metalions exchange their water ligands as much as four-teen orders of magnitude faster than other metals,even when the M–OH2 bonds have the same ther-modynamic strength (e.g. 150 kJ mol–1). Theexplanation for these differences is related to theelectronic and geometrical structures, and theirimportance in the mechanism of action of cisplatinand other metal compounds that interfere with cell-division processes will be outlined. It has beenknown for several decades that the ligand-exchangeprocesses of ions such as Mg(II), Ni(II), Ca(II),Na(I), are very fast indeed (up to 109 sec–1), whereasthe ligand-exchange processes of Pt(II), Pt(IV),Ru(II), Os(II), Ir(III), Cr(III) are very slow; they maytake hours (platinum, ruthenium) or even days(osmium, iridium) at ambient temperatures.

In the early literature, the metal–ligand bond in

Platinum Metals Rev., 2008, 52, (1) 3

4

cases of slow metal-ligand exchange was incorrectlytermed ‘covalent’, or ‘covalent-like’. A better classifi-cation for such bonds is in fact ‘kinetically inert’.Most importantly, the ‘slow’ metal ions such as plat-inum and ruthenium, that exchange some of theirligands within the range of one to two hours, showhigh anticancer activity; these ligand exchange ratesappear comparable to those of many cellular divi-sion processes (2).

The mechanism of ligand exchange reactionsvaries, depending on both the metal and the coordi-nated ligand. Square-planar Pt(II) compoundsusually exchange their ligands via a so-called associ-ative process, where the incoming ligand coordi-nates as a fifth ligand, after which one of the originalligands dissociates. Octahedral Ru(II) coordinationcompounds, on the other hand, tend to lose a ligandfirst (to generate a five-coordinate intermediate),after which the new ligand comes in. Details of ligand-exchange mechanism studies may be found inexcellent overviews by Taube and Van Eldik(12–14).

A schematic presentation of ligand exchangerates for a variety of metal-aqua complexes is depic-ted in Figure 1; the figure is based on early resultspublished by Taube (11).

History of Platinum AnticancerDrugs

The development of cisplatin will be discussedbriefly, from its serendipitous discovery byProfessor Barnett Rosenberg (15) and its reported

anticancer activity (16), up to the most recent paperson the discovery of new platinum compounds in thelast decade. The focus will be on only the last fewyears and on some of the results from the author’slaboratory, with appropriate references to excellentearlier published reviews in this field. After the earlyreview in this Journal by Eve Wiltshaw (1), manyhighly informative reviews followed; those pub-lished before 1999 are referenced in Lippert’sexcellent monograph (17). References (2), (8) and(18–22) are post-1998 reviews on platinum anti-cancer drugs, and deal mainly with cisplatin. Theyare recommended for further reading.

The basic three compounds in worldwide clinicaluse at the time of writing (2007) are cisplatin, 1, car-boplatin, 2, and oxaliplatin, 3. The orallyadministered drug, JM-216/satraplatin, 4, a Pt(IV)compound which is reduced in vivo, is promising interms of treatment regime, since it can be admin-istered without hospitalisation. However, carefulcontrol of the side effects requires frequent out-patient visits (23–24). A recent overview of thecommonly used drugs from a patent point of view isavailable (25).

Platinum Metals Rev., 2008, 52, (1)

Fig. 1 Schematic,logarithmicpresentation ofrelative kinetics ofaqua (H2O)ligand exchange,for a variety ofmetal ions

Cl

Cl

NH3

OAc

OAcC6H11NH2

Pt

4 Satraplatin

10–6 10–4 10–2 100 10+2 10+4 10+6 10+8

Rate of aqua ligand exchange, s–1

Pt4+

Ir3+ Cr3+

Pt2+

Ga3+Al3+Co3+Ru3+

Ru2+

Pd2+Be2+

V2+

In3+ Ln3+

Mg2+

Ni2+

Co2+

Fe2+

Zn2+ Ca2+

Cu2+

Cd2+

Mn2+ Hg2+

Na+

Li+ Cs+

Tetravalent cations

Monovalent cations

Divalentcations

Trivalent cations

Mechanism of Action of CisplatinAfter cisplatin reaches the bloodstream (by injec-

tion or infusion), the drug is well known to betransported all over the body, while few ligand sub-stitutions occur. Any exchange of the relativelymobile chloride ligands, on a timescale of a fewhours, is largely compensated by the presence of theexcess chloride in the blood (about 100 mM). Thesmall fraction of the compound that does hydrolyseis held responsible for such acute toxicities as thatcausing kidney damage. Cisplatin eventually entersalmost all types of cells, by means of passive or evenactive transport via specific receptors. Good evi-dence is now available that in addition to the passiveprocess, the so-called constitutive triple response 1(CTR1) receptor mechanism (by which copper isnaturally transported), assists the platinum species toenter the cell; in the process of excretion, ATP(adenosine triphosphate) plays a role (2).

Upon entering the cells, temporary binding ofcisplatin to one of the membrane components, i.e.phosphatidylserine, has been proposed on the basisof NMR analysis (26). A plausible structure for sucha cisplatin-phosphatidylserine adduct is shown in 5.

At an early stage of mechanistic research on cis-

platin, attention was strongly focused on DNA andits fragments. It soon became clear that the guano-sine (Guo) base binds more rapidly to platinum thando the other bases such as adenosine (Ado). Thiswas explained by a higher basic pKa and by simulta-neous hydrogen bonding of the amine-NH to theO6 of guanosine, as indicated schematically inFigure 2. Careful analysis had already shown a muchlarger proportion of GuoGuo adducts than statisti-cally expected (about two thirds of all platinumbinds at GuoGuo (27)). This binding process hasbeen studied on the mononuclear level (28, 29) andon the dinucleotide and trinucleotide levels (30, 31),including crystal structure determinations (32).When binding to double-stranded DNA, a clearkinked chelated structure is formed, as shown byseveral NMR and X-ray diffraction (XRD) structuredeterminations (33–36). Further work, particularlythat of Lippard (37, 38), demonstrated that certainproteins in the body ‘recognise’ the kinked DNA, asa (direct or indirect) consequence of which the cellmight be killed by apoptosis. A three-dimensionalcrystal structure of such a protein, bound to platinat-ed DNA, has been determined recently (39). Thisshows that the overall kinked structure remainsunchanged and that the protein more or less‘embraces’ the platinated DNA. The link is possiblystabilised by a tryptophane side chain locatedbetween the two coordinated guanine bases.

From the outset of mechanistic studies on cis-platin and its derivatives, it was realised that otherpotential ligands, such as phosphate, carbonate, glu-tathione and peptides, are available in the cellularfluids, in addition to water and DNA. These ligands


O

O OO

O

OO

O–

O

O–

NH3

NH3

CH2

CH2

CH

C17H33

C17H33

CH2

C

HC

H2N Pt

P

5

H3N

HOHPt

HH

HN

HHN

H

NN

N N

Adosugar

7 1

3

H3N

HOHPt

HH

HN

O

NH2

NHN

N N

sugar

7 1

3

Guo

Fig. 2 Platinum binding at the N7 sites ofadenosine (Ado) and guanosine (Guo),indicating that the kinetic approach to Guo iskinetically favoured due to hydrogen bondingwith the O6

may also bind to the platinum. Recently, preliminaryin vitro experiments raised the suggestion (40) thatcarbonato-platinum species may generate DNAspecies different from those proven in earlier in vivostudies (27).

In early mechanistic studies considerable atten-tion was given to the possibility of rapid S-donorligand binding to the platinum species, perhaps asan intermediate (41–43) in transport to the DNA inthe nucleus. Retardation of DNA binding has beenproven (45), although to widely differing degrees fordifferent S-donor ligands. Temporary binding tomolecules such as glutathione and methionine ishighly likely (21, 44). Visual evidence of the progressof intracellular platinum species through the cell wasdelivered by Moolenaar (46), using a cis-platinumdiamine compound carrying a fluorescent label; theprocesses were followed in real time, from enteringthe cell, through entering the nucleus, to leaving thecell via the Golgi apparatus (46).

Other Platinum Compounds andMechanistic Studies

The earliest variations on cisplatin were derivedby substituting different amine and anionic ligands.These studies first produced carboplatin, 2, fol-lowed by compounds with different amine ligandssuch as oxaliplatin, 3, which is now in frequent usein the treatment of colon cancer. Further develop-ments are shown schematically in Figure 3. In

general, ideas for new compounds arise from mech-anistic findings on previous generations of drugs.Below a few important new developments arereviewed, that have recently led to or may lead toclinical applications of platinum drugs.

The obvious starting point for this account isoxaliplatin, 3 (proprietary name Eloxatin®). Thiswas discovered over two decades ago by Kidani (47)and subsequently developed (48), but has onlyrecently been in routine clinical use. This compoundis especially interesting, as tumours which do not orhardly respond to cisplatin, for instance colorectaltumours, are sensitive to it. Nevertheless, almost thesame Pt–DNA adducts have been reported as forcisplatin, including a three-dimensional adductstructure with a double-stranded section ofDNA (49).

Like carboplatin, oxaliplatin and all other sec-ond- and third-generation platinum compoundswith alternative amine and/or anionic ligands haveat least one H-donor function available on one ofthe amine groups. Nevertheless, their steric and lig-and-exchange characteristics are different, especiallyfor the Pt(IV) compounds, as these react very slow-ly. The role of the NH group has been explainedkinetically in terms of its approach to guanosine(Guo) (see Figure 2), in the additional stabilisationof the GuoGuo chelates which are formed, and alsoby hydrogen bonding to a DNA backbone phos-phate (4, 50). This makes them less prone to


NH3Pt

H3N

ClCl

Second generation:Changing chlorides

Third generation:Changing amines

Drug targetingpro-drugs

Oxaliplatin

Trans isomers

Cl Pt NH2(CH2)nNH2 Pt NH2(CH2)nNH2 Pt ClNH3

NH3

NH3

NH3

NH3

NH3

4+

PtCl

Cl N

NCl

Cl Cl

Cl

MeMe

Ru

NH –

O

N

S

Dinuclear and oligonuclear compounds

Other metals, such as Ru;Mixed-metal compounds

NAMI-A

O

O

NH2

NH2

PtO

O

O

OO

O

NH3

NH3Pt

Carboplatin

Fig. 3 Schematic history of the development of platinum drugs. Clinical use of cisplatin started in 1979, of carboplatinin 1989, and of oxaliplatin in 2004. The other compounds are not yet in routine clinical use

reversion by binding to the S-donor ligands in the cell.

The kinetically ‘slow’ Pt(IV) compounds thatwere found to be active against cancer were initiallyassumed to be reduced to Pt(II) in vivo, before bind-ing to the DNA. Later studies have shown thatsome unreduced Pt(IV) compounds may react withDNA and DNA fragments (51), and that traces ofPt(II) catalyse this reaction (52–55). The mecha-nism of reduction also involves the phosphategroups, as proven for guanosine 5'-monophosphate(5'-GMP) (56).

Azido-platinum(IV) complexes have beenreported as possible pro-drugs. Upon ultravioletirradiation, dinitrogen is released by a redox reac-tion and more reactive Pt(II) amine complexes areformed (57, 58). These can react with DNA in vitrolike the familiar Pt(II) compounds (59).

Initially all trans-Pt(II) compounds based on pri-mary amines were found to be inactive; morerecently, it was shown that Pt(IV) compounds wereactive both in vitro and in vivo (60, 61). It has alsobeen shown that sterically hindered amine andimine groups, even when in trans positions, generateactivity in the case of aromatic imines (62, 63) as lig-ands and in aliphatic amines and mixedimine-amine complexes (64–67).

A very important class of dinuclear and trinu-clear compounds (see Figure 3) has been studied indetail by Brabec and Farrell (68–73). The flexiblelink between the platinum ions allows multiplebinding on the DNA chain. This has resulted ininteresting geometrical differences between isomers(74).

Another approach deals with more rigid bridges

between the platinum ions. After the first experi-ments by Kozelka (75), Komeda (76–78) focusedon rigidly bridged dinuclear platinum compounds,containing either pyrazole or triazole bridges.Earlier attempts with imidazoles yielded mono-nuclear compounds upon binding to first-rowtransition metals (79), followed by platinum (80).These compounds proved to be rather inactive, butapplication in trans compounds (81), and with theazolato as a bridging ligand, showed very high invitro cytostatic activities (76, 77, 82). The rationalefor selecting and deploying the bridging azolatogroup is shown in Figure 4. The structural hypo-thesis appears to be valid, as shown by highanticancer activities (77).

More recent studies have proven the hypothesisby high-resolution NMR studies on double-strand-ed DNA with the (pyrazolato)Pt2 unit bound (83),and further confirmed by calculations using densityfunctional theory (DFT) (84).

Ruthenium CompoundsMedicinal ruthenium chemistry was reviewed in

this Journal (85) in 2001 and the early work ofClarke was reviewed in 2003 (86). Recent excellentwork from the Trieste groups on the NAMI-classcompounds (87), and Keppler (88), has boosted thefield of ruthenium anticancer research (6). Only thefollowing interesting classes of compounds withhigh cytostatic activity are mentioned here:(a) New antitumour metastasis inhibitor (NAMI)-

type compounds (see Figure 3 for the structureof the ruthenium cation in NAMI-A).

(b)The so-called azpy (azopyridine) compounds,where different isomers show significantly


Active, crosslink Inactive, crosslink Inactive, NO crosslink Active, crosslink

H3NH3N Pt

H3N Pt PtL

LL

Pt

Pt

NN

NH3

small distortion large distortion small distortion small distortion

Fig. 4 Rationalebehind the design ofthe azolato-bridgeddinuclear platinumcompounds, leadingto a crosslink, and avery small DNAdistortion

different cytostatic activity. The structures andactivity indicators are given in Figure 5.

(c) The organometallic half-sandwich compoundsof formula [Ru(sandwich)(diamine)Cl], wherefine-tuning in the amine ligand is very importantfor the activity (89–91); again hydrogen bondingplays important roles here.The NAMI-type compounds all contain Ru(III),

and it is believed that prior to biological, cytostaticaction, reduction to Ru(II) may take place.

The mechanism of action of the rutheniumcompounds is hardly known, and even the fact thatDNA is an important target is not sure as yet (92).

Mixed-PGM CompoundsCombination therapy using platinum and ruthe-

nium compounds is of course possible (93). If twodifferent metals can be linked, in a kinetically inertway, by a ‘spacer’ of variable length, then a wealthof new compounds is possible with a view to fine-tuning performance. For platinum and ruthenium,a few cases have already been reported (94, 95),including a three-dimensional structure determin-ation, 6, a dinuclear cationic species containingRu(II) and Pt(II), with a variable spacer.

Although the antitumour activity of this com-plex is limited, it has prompted new research on

related platinum-ruthenium compounds. Anotherpossibility is to combine the ‘slow’ metal with a‘faster’ metal, such as Cu(II). The latter is a wellknown DNA cleaving agent, when bound tophenanthroline-based ligands (96).

Concluding Remarks and FutureDevelopment

The work selected and summarised above hasshown that the ‘heavy metals’ platinum and ruthe-nium, when coordinated to the appropriate ligands,may act as powerful anticancer drugs. The fact thatthese metals are ‘slow’ in ligand exchange reactions,and exchange many of their ligands within the sametimescale as that of cellular division processes, indi-cates that these compounds are not dissociatedbefore any of their biological targets are reached.The target for the platinum compounds is nowaccepted to be DNA, to which kinetically inert


2-phenylazopyridine = azpyP A

NN

N

ClCl

Ru

P

PA

A

ClCl

Ru

P

AA

P

ClP

Ru

P

AA

Cl

ClA

Ru

P

PA

Cl

ClCl

Ru

A

AP

P

tc(c)α

++++

cc(t)γ

+++

cc(c)β

+/–

ct(c)ε +/–

tt(t)δ +/–

Fig. 5 Five different isomersof a bis(azpy)Ru(II) complexand their relative cytostaticactivity (++++ = very active;t = trans; c = cis for eachpair of ligand atoms (anionsin parentheses))

N N

N NRu O O O N

N

NPt Cl

3+

NN

6

attachment of the platinum compound allows thestart of a cascade of reactions. The cascade even-tually leads to apoptosis or necrosis of the tumourcells and repair of the non-tumour cells (2). Itshould be noted that DNA damage is sustainable ina non-replicating or resting cell, and that apoptosiswill be induced only when the cell is growing anddividing.

Although the kinetics of ruthenium coordina-tion chemistry are comparable to those ofplatinum, and even though a number of activeruthenium compounds do react with DNA andDNA fragments (97), the mechanism of action forthe ruthenium compounds is currently far lessunderstood. Targets other than DNA may play arole as well here (6, 92).

Future development in this field is likely tomove towards bifunctional and trifunctional com-pounds, with other parameters such as inter-calation, photosensitivity and redox propertiescoming into play.

Finally it should be noted that also other noblemetals, such as gold and rhodium (98), are compa-rably slow in ligand exchange. The present briefoverview is far from comprehensive; the focus hasbeen on some issues of ligand exchange kineticsthat platinum and ruthenium have in common, andalso on topics not frequently reviewed. Finally, thisreview has been tuned to the general readership ofthis Journal, and less so to the specialists in the fieldof anticancer chemistry. The extensive referencelist, including some specialist reviews, should helpthe interested reader to find more details.Reference (99) (citation added in proof) is a veryrecent overview of the field.

AcknowledgementsThe author thanks the many students and post-

doctoral workers who contributed to the researchhighlighted in this paper. Their names are listed inthe references as co-authors of previous papers.The following are gratefully acknowledged: sup-port and sponsorship contributed under EuropeanCOST Actions D20/0001/00, D20/0002/00 andD20/003/01 (Metal Compounds in the Treatmentof Cancer and Viral Diseases; 2001–2006); a gener-ous loan of potassium tetrachloridoplatinate(IV)

(K2PtCl4) and ruthenium(III) chloride hydrate(RuCl3·3H2O) by Johnson Matthey PLC, U.K.;continuous support from the NetherlandsOrganisation for Scientific Research (NederlandseOrganisatie voor Wetenschappelijk Onderzoek;NWO) and its chemical council (ChemischeWetenschappen; CW).


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The Author

Professor Jan Reedijk has held the chair of Inorganic Chemistry atLeiden University since 1979. He was the Director of the LeidenInstitute of Chemistry between 1993 and 2005. After obtaining anM.Sc. and Ph.D. from Leiden University (1968), he lectured at DelftUniversity of Technology until taking up his present post. His currentresearch interests include the coordination chemistry of transitionmetal ions, and bioinorganic chemistry (including active-site structureand mechanism, models and metal-DNA interactions). He has (co)-authored over 1000 patents and research publications in refereedjournals (1966–2007), and has supervised over 130 postdoctoralworkers and graduate students (1973–2007).

Platinum Metals Rev., 2008, 52, (1), 12–20 12

The Grove Fuel Cell Symposium and exhibitionwas again held at the Queen Elizabeth IIConference Centre in Westminster, London, onthe 25th to 27th September 2007 (1). The confer-ence, the tenth in the series over 18 years (2),attracted 375 delegates from 32 countries. Whilethe conference remains the largest fuel cell gather-ing in Europe, attendance was slightly less than in2005, which may have reflected the scheduling ofthe 2007 Fuel Cell Seminar & Exposition, heldonly a fortnight later in San Antonio, Texas, and‘f-cell 2007’, almost simultaneously on 24th to 25thSeptember at Stuttgart, Germany. A further 800people attended the trade exhibition held in paral-lel with the Symposium. This exhibition wasremarkable for the proportion of working exhibitsand vehicles – a sign of the considerable progressbeing made towards commercialisation by the fuelcell industry. A large number of fuel cell types havebeen developed to the semi-commercial demon-stration stage, and in several cases production isramping up, which will bring about the long await-ed cost reductions to make fuel cells economicallycompetitive.

Because of the wide range of fuel cell types andapplications being developed, and in line with thecoverage of this Journal, this review is mainly

restricted to those associated with the use of theplatinum group metals (pgms).

Grove Medal PresentationThe event was formally opened by Bronwen

Northmore (Head of Cleaner Fossil Fuels at theU.K. Department for Business, Enterprise andRegulatory Reform), on behalf of Malcolm Wicks,the U.K. Energy Minister, who was attending theLabour Party Conference. The U.K. Governmentstrategy, initiated by the Climate Change Bill, isintended to encourage energy savings and supportlow carbon technologies. This has led to the estab-lishment of an Energy Technology Institute whichwill investigate distributed energy generation andlow carbon transport, together with a technologydemonstration programme.

Bronwen Northmore presented the GroveMedal to Haldor Topsøe, founder of HaldorTopsøe A/S of Denmark. The medal was accept-ed on his behalf by Professor Jens Rostrup-Nielsen, since Haldor Topsøe was unavoidablydetained on business. At the age of 94, HaldorTopsøe is still actively engaged in running thecompany and hence his talk was also presented byProfessor Rostrup-Nielsen, who explained that hecreated the vision and pushed people to haveambitions in their work. Haldor Topsøe A/S wasset up to develop chemical processing plant, con-centrating on catalysis and materials technology,and has built several types of hydrogen productionsystem. The Topsøe philosophy is to anchor theirbusiness on a fundamental understanding of theprocesses involved, which has involved fundamen-tal research as well as exploitation of this work.

Topsoe Fuel Cell has been collaborating withthe Risø National Laboratory in Denmark to devel-op solid oxide fuel cells, on the understanding thatthe final products must compete in cost terms.Performance of the fuel cells has been successfully

The Tenth Grove Fuel Cell SymposiumFUEL CELLS IN A CHANGING WORLD – A PROGRESS REPORT

Reviewed by Donald S. CameronThe Interact Consultancy, 11 Tredegar Road, Reading RG4 8QE, U.K.: E-mail: [email protected]

A fuel cell powered Micro Taxi built by CoventryUniversity, U.K.

DOI: 10.1595/147106708X263672

demonstrated, but so far they have not been cost-competitive. Steps are being taken to eliminatescrap in manufacture, and to reduce the number ofunit operations in production. A factory is beingbuilt in Lyngby, Denmark, with a capacity of 10MW year–1, which is due to begin production in2008. The development is expected to take 8 to 10years, which is similar to the timescales for otherchemical processes developed by Topsøe. Despitehis age, Haldor Topsøe takes a long-term view,as typified by his current reorganisation of thecompany structure, and the belief that fuel cellsmust compete economically with other technolo-gies, while providing other benefits such as fuelflexibility and efficiency.

Challenges and SolutionsIn the first Plenary Session, in a talk entitled

‘Environment and Energy Challenges’, ProfessorJim Skea (UK Energy Research Centre) outlinedthe challenges presented by global warming, andthe increasing demand for energy due to increasingaffluence worldwide. A further factor is becomingimportant for the European Union – security ofsupply. Between now and 2030, there will be a50% increase in oil demand, most of which willcontinue to be met from the Middle East, while by2030, 80% of natural gas will come from sourcesoutside the European Union. The UnitedKingdom became a net oil importer in 2006, dueto a run-down of North Sea Gas supplies.Professor Skea outlined the choices available tominimise global warming. He concluded that theneed to do this is pressing, but that the means tomeet the need are available if mankind takes upthis huge challenge.

Jan van Dokkum (UTC Power, U.S.A.)acknowledged that the United States is at lastrecognising the existence of climate change. Aswell as population increases, an additional factorto be addressed is that people are increasingly liv-ing in cities. Urban dwellers use more energy, andare dependent on secure power supplies. Between1970 and 2030, the proportion of urban dwellers isexpected to increase from 35% to 60% worldwide.Capitalising on almost 50 years of experiencegained in the space programme and other fuel cell

developments, United Technologies Corporationhas for the past 15 years produced a 400 kW phos-phoric acid fuel cell (PAFC) system, which hasnow demonstrated 10 year lifetimes for the cellstack. Stacks are guaranteed for 5 years (44,000hours) and currently last 50,000 to 70,000 hours.UTC are continuing to develop PAFCs, with a tar-get to double power output and lifetimes whilehalving cost as compared with early cells, with aview to producing an economically viable station-ary power system.

UTC is also developing polymer electrolytemembrane (PEM) fuel cells for buses. This appli-cation avoids many of the near-term barriers toautomotive applications such as power density,cost and refuelling. Buses with UTC Power fuelcell systems are in revenue service, and their cen-tralised refuelling facility is contributing to thedevelopment of a hydrogen supply infrastructurewhich will benefit other automotive applications.In general, government support is needed onaspects such as codes and standards, to facilitateinstallation of fuel cells, and incentives to encour-age more efficient use of energy. To date, fewerthan 1000 fuel cell vehicles have been produced,so it is hardly surprising that costs currently com-pare unfavourably with those of internalcombustion engine (ICE) vehicles, tens of mil-lions of which are built each year (3). However,UTC is of the opinion that the cost target ofU.S.$45 kW–1 set by the U.S. Department ofEnergy for automotive fuel cell power plants in2010 (U.S.$30 in 2015) is achievable with massproduction (4). The cost of hybrid ICE/electricvehicles is rapidly decreasing, and fuel cell vehi-cles are inherently simpler than these. One ofthe main barriers to the adoption of automotivefuel cells is the need for a hydrogen refuellinginfrastructure.

Michael Bode (CFC Solutions GmbH,Germany) outlined progress being made in sta-tionary power generation. His company hasdeveloped molten carbonate fuel cells, which arebuilt up in 220 kW modules and demonstratedworldwide in 40 installations ranging from 200 kWto 2000 kW rating, operating on a range of fuelsincluding renewable energy sources. Bode outlined


the challenges that have been addressed toimprove reliability and cost, and to commercialisethe system.

Road VehiclesAlthough progressing more slowly than predict-

ed some years ago, light passenger fuel cell vehiclesare being developed by most of the major auto-motive producers worldwide. James Wilkie (ACALEnergy Ltd., U.K.) argued that the current popu-larity of internal combustion engine/hybridelectric vehicles (ICE/HEVs) provides a valuablelearning experience for fully electric models.Increasingly stringent pollution legislation is mak-ing it more expensive for ICEs to meet therequirements, while the mass production of hybridpetrol/electric and diesel/electric vehicles is bring-ing down the costs of compliance. Over 1 millionHEVs have been produced to date, compared withthe small number of prototype fuel cell vehiclesworldwide. Sales of the Toyota Prius and otherhybrid models alone amount to 400,000 to 500,000vehicles worldwide per year. This is still small com-pared to the 57 million ICE vehicles produced, butit is sufficient to bring down production costs, andthe perceived environmental friendliness of hybridvehicles has been of enormous brand value to themanufacturers. Regarding complexity, the fuel cellvehicle has only one power source, and will bene-fit from developments for HEVs in batteries,motors and features such as regenerative brakingand lightweight body design. Familiarity with elec-tric drive systems will facilitate consumeracceptance of fuel cell models. Automotive fuelcells still face challenges in terms of hydrogen stor-age on board, and stack costs and availability, aswell as development of a chain of publicly availablehydrogen filling stations. Wilkie suggested thattechnology such as the through-flow cathodesbeing developed by ACAL Energy Ltd. in combi-nation with aqueous redox mediator systems couldreduce the need for pgm catalysts as well as facili-tate the cooling of the fuel cell stack.

Zoe Jennings, Daniel Pizarro and Mike Weston(London Hydrogen Partnership, U.K.) revealedplans for a collaboration by Transport forLondon, the Metropolitan Police, the London Fire

Brigade and other organisations to run trials on 10buses and 60 light vehicles. Nine European cities,including London, were involved in the CleanUrban Transport for Europe (CUTE) bus pro-gramme which has now been completed, and thiswill be followed by operating a whole city busroute from the summer of 2009 for 18 hours aday, 365 days a year.

Large Stationary ApplicationsPAFCs catalysed by platinum are being advo-

cated for a range of applications where wastehydrogen is available. Leo Blomen explained howHydroGen Corporation, U.S.A., has been set upwith private finance to exploit the air-cooled tech-nology originally developed by Westinghouse in a$150 million programme which is being revivedand adapted. The company will focus on a smallnumber of very large customers, with a fuel cellunit rating likely to be 5 to 30 MW, comprisingmultiples of modules each of 400 kW output. Thefirst two 400 kW modules have already been pro-duced. There are numerous hydrogen wastestreams originating from sources such as chloralka-li and chlorate plants, coke oven gases, ethylene offgas, ammonia and methanol production plants.These are often located at sites near harbours suchas Houston-Galveston, Rotterdam, Shanghai andLong Beach, and the hydrogen-rich byproducts arefrequently vented. This waste hydrogen can beused to provide heat, water and electric power, aswell as financial credits and incentives.

A measure of the durability of the PAFCs is pro-vided by the observation that a 15 year old 400 kWfuel cell module built by Westinghouse has beentaken out of store, refilled with phosphoric acid andrestarted, the open circuit voltage being within 1%of the original. HydroGen opened a factory inVersailles, Pennsylvania, in 2006 with an annualproduction capacity of 4 MW, which is intended toramp up to 100 MW year–1 by 2010. Their firstinstallation will be a 400 kW demonstration unit atAshtabula, Ohio, in a commercial chloralkali plantoperated by ASHTA Chemicals Inc.

A similar application was reported by EricMiddelman (NedStack fuel cell technology BV, TheNetherlands), using PEM fuel cells to recover


energy from waste hydrogen originating in chlor-alkali plants. NedStack was formed in 1998 to usetechnology developed by Akzo Nobel, and is thelargest European producer of fuel cells. The tech-nology uses thin moulded thermoplastic separatorplates with microchannel flow fields, which havedemonstrated over 200,000 hours of operationwithout deterioration. The company also producesfuel cells for other stationary and transport applica-tions, 98% of which are exported. The chlorine andchlorate industries often produce waste hydrogenequivalent to 25 MW capacity from a single plant,while hydrogen overcapacity in the U.S.A. amountsto over 3000 MW. The NedStack fuel cell moduleseach produce 50 kW (80 A at 630 V) DC power,while the system delivers 380 to 400 V AC powerback to the grid. NedStack have demonstrated a120 kW plant operating at Chemiepark Delfzijl,The Netherlands, as part of a petrochemical pro-duction complex, where it meets normal industrysafety standards. Durability required for industrialproduction plants is in excess of 175,000 hours forthe whole system, and at least 40,000 hours for thefuel cell stacks. Rates of voltage decay of less than1.8 μV hour–1 have been observed (i.e. less than10% voltage loss in 40,000 hours), while the best

stacks have given 0.1 μV hour–1. Typical behaviourobserved in production stacks is a more rapiddecay in the first 400 hours, which then stabilises atless than 0.2 μV hour–1.

Significantly, NedStack state that while theirPEM fuel cells are heavy duty models designed tobe robust for the chemical industry, the cost ofplatinum they contain is less than 60 € kW–1 with-out recycling, or less than 3 € kW–1 with recycledmetal. Due to the use of otherwise waste hydrogen,the payback on the system is less than 3 years,although the economic feasibility will obviouslydepend on factors such as the competing cost ofpower from the grid, hydrogen purity, local fund-ing and support. Cost of the system is currently 700 to 1500 € kW–1, which is scheduled to bereduced to 75 to 250 € kW–1 by 2010. At 250 € kW–1 the system is directly competitive withdiesel engines. Overall, the project is well on sched-ule to meet durability, safety and economic targets.

Transport ApplicationsPapers were presented on several novel applica-

tions for PEM fuel cells. Paul Adcock (IntelligentEnergy, U.K.) described his company’s range offuel cells, some of which are intended for passen-ger automotive power. Their model EC200-192,which has a stack active area of 200 cm2, and 192cells, can provide a maximum of 17 kW at 90 A.This has demonstrated a lifetime of over 5000hours, with an average voltage decay rate of 3.2 μVhour–1 in a 23 hour operating day with 1 hour shut-down. The metallic bipolar separator plates offerthe advantages of compactness with low voltageloss characteristics.

A 10 kW fuel cell engine intended for thePeugeot Partner light van has an efficiency of47%, and is capable of starting from –25ºC. It canprovide 80 A after 60 seconds and is almost self-heating. The company is also developing a 75 kWhigh-power PEM fuel cell in collaboration withPSA Peugeot Citroën/Bosch, which is capable ofstarting from –40ºC. The fuel cells are all designedto operate on industrial grade hydrogen of 99.99%purity, and ambient air. Although the fuel cells arestill only available in limited quantities, the eventu-al costs should meet the U.S. Department of


NedStack 50 kW fuel cell module, used in the demon-stration project at Chemiepark Delfzijl, The Netherlands(Courtesy of NedStack)

Energy target for automotive fuel cells, once massproduction levels are achieved.

John Heinzel (U.S. Department of the Navy,Naval Sea Systems Command (NAVSEA))detailed the range of fuel cells being investigatedby the United States Navy. One of the constraintson any military fuel cell is the need to be capable ofoperation on the high-sulfur logistics fuels general-ly used. Other requirements are high reliability andresistance to vibration and electromagnetic pulses,as well as to possible salt contamination of the inletair. Heavy marine fuel can contain up to 1.5% byweight of sulfur, while JP5 jet fuel contains up to0.3 ppm by weight. The U.S. Navy is evaluatingvarious fuel cell technologies, including a 625 kWsolid oxide fuel cell, operating on sulfur contami-nated fuel, and a 500 kW PEM fuel cell system. A50 kW PEM fuel cell is being used together with a250 kW autothermal reformer to demonstrateoperation on fuel containing up to 1000 ppm sul-fur. Eventually power generator units of 2500 kWrating are being considered, consisting of 5 × 500kW fuel cell modules, in cabinets occupying a vol-ume of 7.31 m × 2.44 m × 2.44 m. Small units areexpected to be available during the next 2 years,while 250 kW units are expected to be available inthe 2012 to 2015 timeframe. The fuel cell stacksare required to have a 10,000 hours minimum life-time, even when exposed to salt air; vibration andmechanical shock are still issues.

The marine market for fuel cells is potentiallyvery large, with 87,000 commercial vessels at sea.The majority have relatively small propulsion units,rated at less than 2 MW, which are built at the rateof over 5000 year–1. There are also more than10,000 vessels in the small to midsize range (up to10 MW). Marine diesel engines produce around4.5% of the NOx emissions and 1% of the partic-ulates from all mobile sources. These emissions area particularly sensitive issue when the vessels are inport, and for this reason the EnvironmentalProtection Agency (EPA) and California AirResources Board (CARB) are considering regula-tions for engine cleanliness.

Nina Lapeña Rey (Boeing Research andTechnology Europe, Spain) gave details of a pro-ject called the Fuel Cell Demonstrator Airplane,

intended to demonstrate for the first time an air-craft propelled in straight level manned flight withfuel cells as the sole energy source. A SuperDimona HK36TTC glider from Diamond AircraftIndustries in Austria has been modified to accept aPEM fuel cell system provided by IntelligentEnergy, in combination with a 25 kWe lithium-ionbattery from SAFT Aviation. The fuel cells canprovide a gross output of 18 kW from each of twoEC168 stacks, and the battery has been sized toprovide up to 50 kW power for 5 minutes for safe-ty purposes. The aircraft is intended to use bothpower sources for the 7 minutes required for take-off and the climb to 1000 feet (305 m), after whichthe fuel cell will provide 18 kW to maintain thecruising speed. Fuel will be provided by a hydrogenstore at 5000 psi, and the weight distribution of thecomponents has been arranged to maintain thecorrect centre of gravity of the aircraft. The air-plane is currently undergoing bench testing tothoroughly check the performance and reliabilityof all components and overall systems prior toground and flight tests. It is hoped to begin thesein late 2007.

In a talk entitled ‘Near Term Fuel CellLocomotives for Urban Rail Applications’, ArnoldMiller (Vehicle Projects LLC, U.S.A.) gave detailsof an industry-government consortium developingtwo prototype fuel cell hybrid locomotives forswitching (shunting) and road switching. The for-mer operate only within rail yards, while the latterare required to move short trains for short dis-tances along running lines from one location toanother. The object is to demonstrate locomotiveswith low pollution characteristics for use in envi-ronmentally sensitive areas such as seaports, andalso to provide mobile generating grid capacity formilitary or civil emergencies. The project involvesusing two commercially available Green Goat®

diesel/battery hybrid locomotives and adaptingthem with 250 kW Ballard PEM powerplantsdeveloped for the Citaro buses used in the CUTEproject. Hydrogen pressure stores are provided byDyneteck Industries, while BNSF Railways areproviding funding, integration and testing facilities.The project is also supported by the U.S.Department of Energy and Department of



Defense. The switcher locomotive has a minimumweight of 127 tonnes, which is necessary to pro-vide adequate traction. Since the fuel cell hybridlocomotive is lighter than the diesel equivalent,some 9 tonnes of steel ballast is required. The fuelcell, operating in parallel with the existing lead acidtraction batteries, provides up to 1200 kW powerfor starting and acceleration, while a steady 75 kWis needed throughout the duty cycle of 10 hours, atotal of 750 kWh. The first locomotive is expectedto be completed within the next 6 monthsfor evaluation.

Consumer Electronic DevicesThere are rapid strides being made towards fuel

cell power for consumer electronic devices such asmobile telephones and laptop computers, withmost of the world’s major electronic device manu-facturers involved in development projects.Several systems use PEM fuel cells with hydrogenpressure vessels and hydride stores; others usedirect methanol fuel cells (DMFCs). At present notechnology appears to be ‘head and shoulders’above the others, while several developmentsappear to be approaching the commercial stage. Itis likely to be consumers who decide which willultimately be successful. Considerable effort isbeing devoted to developing and demonstratingrefuelling systems for each type of cell, as befitsproducts available to the public.

Designing a viable alternative to advanced bat-tery packs is a formidable challenge, as explainedby Ged McLean (Angstrom Power Inc., U.S.A.).The convergence of voice, data and multimedia inhandheld formats has created a demand foradvanced power supplies that exceed the capabili-ties of lithium batteries. However, any alternativewill need to be of similar size and weight to thebattery, since no original equipment manufacturerwill sacrifice performance. The alternative musttherefore provide not only an adequate power rat-ing, but quality of power – for example, GSMdevices require 217 Hz frequency and a peakpower of 4 times the continuous rating. Despitethe perception that consumer devices have shortlifetimes, the power source will need a 2 year life,with 1000 connect/disconnect cycles, as well as

withstanding thermal cycling, and a 15,000 hourmixed duty cycle with long open circuit standbyperiods. In addition, the shelf life may be up to2 years, representing the time spent in the distrib-ution chain for products sold worldwide.

One factor in favour of fuel cells is that the fuelstore is separate from the fuel cell. Recent safetyrecalls of high-power lithium batteries have drawnattention to the possible dangers of incorporatinglarge reserves of power inside sealed packs.Angstrom Power have developed complete sys-tems comprising thin film fuel cells less than 1 mmthick, with a metal hydride fuel store, DC–ACinverter etc. in one compact package. In 2005 theydeveloped a 5 V system with 1.2 W continuousoutput, 2.4 W peak power, with short peaks of 4W, and a total volume of 25 cm3. This equates to500 Wh l–1, as compared with the 400 Wh l–1 oflithium-ion batteries. Angstrom Power have pro-duced an 18 cm3 palmtop battery power packwhich will fit into the battery bay, and plan a10 cm3 package as a cell phone replacement. Theelectronics industry is working to obtain approvalfor the carriage of various fuels on board aircraft,and flight testing is being carried out in Canada.Thus the regulatory framework is being preparedfor the roll-out of fuel cells as consumer electron-ic power supplies.

The Toshiba Corporation, Japan, has its ownview of micro fuel cells for electric gadgets, whichwas presented by Fumio Ueno. Toshiba have cho-sen DMFCs, refuelled by means of a cartridge ofpure liquid methanol which can be carried separate-ly. High-purity methanol is specified to ensuredurability. The cartridge is designed to be leakage-and child-proof and can only be discharged into thefuel cell; the intention is that one cartridge may beused to replenish several types of devices. TheInternational Electrotechnical Commission (IEC)is drawing up an international standard formethanol cartridges which will help to make themwidely available and facilitate their being carried onpassenger aircraft. It will also enable several DMFCmanufacturers to share refuelling cartridges.

Toshiba built a laptop which could be poweredby an 18 W fuel cell for 10 hours with one fillingof methanol. The fuel cell operated in parallel with


a lithium battery for peak power, while the fuel cellprovided a slight excess over normal demand torecharge the battery. The Toshiba DMFC (45 mm× 78 mm × 7 mm) for a mobile telephone provides16 hours of continuous talk time.

A novel method of hydrogen generation hasbeen demonstrated by Samsung Electro-Mechanics, Korea, explained Jae Hyuk Jang, in histalk entitled ‘Development of Micro-HydrogenGenerator for Mobile Fuel Cells’. The system con-sists of a disposable cartridge containing aninexpensive aluminium anode and a hydrogen-evolving cathode, surrounded by water. When thesetwo electrodes are joined together electrically,hydrogen is evolved from the cathode, and the alu-minium is oxidised to hydroxide, while the rate ofhydrogen evolution can be controlled by the currentpassed. The product hydrogen can be fed to a PEMfuel cell which powers electronic devices. TheSamsung target is for a device providing 30 Whcapacity consisting of a 50 cm3 cartridge with a 20cm3 fuel cell. The company is developing recyclingstrategies for the disposable cartridges.

Jim Balcom (PolyFuels Inc., U.S.A.) explainedtheir reasons for optimism in developing DMFCtechnology. Hydrogen PEM fuel cells for automo-tive use have progressed from power densities ofaround 0.56 W cm–2 in 1990 to 0.77 W cm–2 in 2005,while at the same time, platinum loadings on theelectrodes have fallen from a typical 8 mg cm–2 to0.5 mg cm–2 in the same time period. Lithium-ionbatteries for electronic devices have improved lin-early in their volume energy density from about 200to 300 Wh l–1 between 2004 and 2006, while energydensities from DMFCs have improved from 50 to200 Wh l–1 in the same period. In terms of volumepower density, PolyFuel DMFC stacks haveimproved from 170 W l–1 in 2003 to500 W l–1 in 2007. The point is rapidly approachingwhere the fuel cell will outstrip the lithium-ion bat-tery in performance and convenience of operation.PolyFuel is collaborating with leading notebookcomputer manufacturers and Johnson Matthey FuelCells to develop catalyst and membrane electrodeassemblies, and also with a number of other organ-isations to produce standard fuel specifications andcartridge designs and to get them approved.

Self Powered Electronic ChipsProfessor Helmut Reinecke (Institut für

Microsystemtechnik (IMTEK), Germany)explained in his presentation that the integrationof fuel cells onto microchips is now a possibilityfor applications such as verifying the history offood storage conditions. An inexpensive powersupply is needed to power electronic temperaturesensors and transmitters for up to 6 months dur-ing storage. Overall power demand is an averageof 3 μW for this period. One way to meet this isby using hydrogen stored in palladium as fuel, withatmospheric air as oxidant. It is possible to useCMOS (complementary metal oxide semiconduc-tor) processes to apply thin (80 μm) palladiumlayers to monolithic integrated chips. A layer ofNafion® proton-conducting polymer membrane isthen deposited on top of this, followed by aplatinised carbon layer as the cathode. Tiny fuelcells are formed, each about 4 mm × 4 mm inarea, located within a small reservoir containingwater. This configuration will yield 70 μW output(a power density of 438 μW cm–2) with a lifetimeof 180 days. The system can be charged withhydrogen by imposing a current to cause electrol-ysis, with an efficiency of energy stored aspalladium hydride of about 65%.

Exhibition and Poster SessionOne noticeable feature of the Exhibition was

the number of hardware and equipment items ondisplay, ranging from fuel cell powered vehicles,including a bus and a large motor-home incorpo-rating an auxiliary power unit, through residentialcombined heat and power supplies resemblingdomestic gas boilers, down to tiny power sourcesfor electronic devices. Over 800 visitors enjoyed avisit to the exhibition, in addition to the confer-ence delegates. This provided a forum fordiscussions between manufacturers, suppliers andpotential customers.

Over 130 high-quality posters were presented,more than two dozen of which involved PEMfuel cell catalysts and components and also directmethanol and ethanol oxidation requiring the useof pgms. Six prizes were awarded for posters ofexceptional content and presentation. Two of


these concern PEM fuel cell technology, and oneimprovements to DMFC performance, all ofwhich utilise pgm catalysts.

A Comparison with the First GroveSymposium

This Tenth Grove Fuel Cell Symposium pro-vided an opportunity to assess the progress of thefuel cell industry in the intervening 18 years sincethe first meeting (2). Professor Gary Acres,Honorary President of the Grove SteeringCommittee, and former Grove medalist,explained that the first meeting was held in 1989to celebrate the 150th anniversary of the inven-tion of the fuel cell by Sir William Grove, aBritish scientist and lawyer (5). The aim of theSymposium was to provide a forum for theappraisal of the technology, and how fuel cellsmight influence future energy strategy. At thetime, the U.S. and Japanese governments activelysupported fuel cells, although there was no equiv-alent support in Europe.

Professor Acres recalled that in the early meet-ing, the technology was dominated by PAFCs,with molten carbonate and solid oxide fuel cellsstill at the development stage. There was a gener-al consensus that large power generators appearedto offer most promise, since smaller units neededas much manufacturing effort as larger devices.Even for these large generators, mass productionwas required to bring down prices to competewith conventional devices. It was anticipated thatthe superior efficiency and cleanliness of fuel cell

generators would lead to the installation of 2000MW of capacity by the year 2000. Although thisparticular promise has not been fulfilled, technicalinnovation and potential markets for smallportable fuel cells and consumer electronics appli-cations now exist that were not even dreamed ofat that time. There are several new areas in whichfuel cells show great potential. These range frommicro and portable applications exploiting thehigh power density obtainable from PEM fuelcells and DMFCs, to the commercial possibilitiesof fuel cells for residential combined heat andpower. The PEM fuel cell technology developedby General Electric, used for the first Geminispace flight, was languishing by the late 1980s,only to be transformed in terms of performanceand cost for automotive applications since thefirst Grove Symposium. It is also interesting thatPAFCs, which have had slow sales for some time,are now re-emerging as they are modified toreduce costs, capitalising on their longevity andhigh engineering development.

One of the major differences between the Firstand Tenth Symposia is that much greater empha-sis is now placed on pollution control, and it isbecoming increasingly expensive to adapt theinternal combustion engine and large power gen-erators to meet more stringent regulations. Inaddition, greater recognition is paid to energy con-version efficiency and also the capability to adaptto alternative and renewable energy sources. Itis now recognised that fuel cells will have tobecome financially competitive with conventional

A fuel cell minibus exhibited by theUniversity of Glamorgan, U.K.


generators if they are to be widely adopted.Although greater efficiency and cleanliness makea cost premium viable, this has been estimated atno more than about 15% compared to conven-tional generators.

ConclusionIt is evident that fuel cells are already being

established on a commercially viable basis inmany niche markets, including military and stand-by power supplies. Fuel cells are gradually beingaccepted for other applications. There were sever-al references at the Symposium to the ‘valley ofdeath’ which represents a barrier to new products.Until devices are mass produced, their unit costremains high, but until costs reduce, sales vol-umes remain limited. It is hoped that in severalsectors, the numbers of fuel cells currently beingmanufactured and evaluated are enabling this bar-rier to be crossed to launch successful productscommercially. The pgm costs quoted by NedStackindicate that with recycling, platinum catalysts donot constitute a significant proportion of theaggressive U.S.$30 kW–1 target quoted by the U.S.Department of Energy for PEM fuel cells in 2015(4). Platinum catalysts are likely to continue todominate the low-temperature fuel cell market inview of their superior performance.

The Eleventh Grove Fuel Cell Symposium isscheduled for September or October 2009 inLondon. Technical developments in the fuel cellfield will be reported in Fuel Cells Science andTechnology 2008, which will be held on the 8thand 9th October 2008 at the DanishConfederation of Industry Conference Centre,Copenhagen, Denmark (6).

The Reviewer

Don Cameron is an independentconsultant on the technology of fuelcells and electrolysers. As well asscientific aspects, his interests includethe standardisation andcommercialisation of these systems. Heis Secretary of the Grove SymposiumSteering Committee.

Delegates to the Grove Symposium were able to enjoy spectacularpanoramic views of central London and Westminster from the windows ofthe Queen Elizabeth II Conference Centre

References1 The Grove Fuel Cell Symposium:

http://www.grovefuelcell.com/2 Platinum Metals Review: Nuggets, Fuel Cells:

http://www.platinummetalsreview.com/dynamic/booklist#fuelcells

3 Auto Industry, World Vehicle Production Since1997 by Region:http://www.autoindustry .co.uk/stat is t ics/production/world

4 N. Garland, ‘U.S. Department of Energy Fuel CellSub-Program’, Fuel Cell Seminar, Presentations, SanAntonio, Texas, 16th–19th October, 2007:http://www.fuelcellseminar.com/2007_seminar.asp

5 J. Wilson, W. Wilson and J. M. Wilson, “WilliamRobert Grove. The Lawyer Who Invented the FuelCell”, Metolius Ltd., Hereford, U.K., 2007

6 Fuel Cells Science and Technology 2008:http://www.fuelcelladvances.com/

Inorganic compounds have been used in medi-cine for thousands of years, often without aknown molecular basis for their mechanism ofaction, and with little attempt to design them. Thedesign of coordination (metal) complexes is not aneasy task. The organic chemist often deals withdiamagnetic compounds which are both kinetic-ally and thermodynamically stable, and benefitsfrom the use of well developed speciation tech-niques, especially 1H and 13C nuclear magneticresonance (NMR) spectroscopy. For metal com-pounds the situation is more complicated. Ligandsubstitution and redox reactions can be facile, canoccur over very wide timescales, and are not soeasily followed by conventional techniques, es-pecially under physiologically relevant conditions(for instance, at micromolar concentrations). Butthe challenge is real and worth exploring. We neednew drugs with novel mechanisms of action.Inorganic chemistry offers that possibility.

Platinum Anticancer DrugsTwo areas of work have highlighted the poten-

tial of inorganic chemistry in recent years: theplatinum anticancer field and gadolinium com-pounds, used as contrast agents in magneticresonance imaging (MRI). Both of these are wellcovered in this new book. Platinum commandsabout forty pages. This is warranted. Platinumcompounds are now the world’s best-selling anti-cancer drugs – they have billion-dollar sales eachyear. If you are not familiar with atomic structure,types of chemical bonds, oxidation states, coordi-nation geometries, isomerism, electronicstructure and magnetism, then there are some onehundred pages (just over a quarter of the book) of

introduction to help you, including thebackground on square-planar platinum com-plexes needed to understand the mechanismof action of the first platinum complex to be approved for clinical use: cisplatin (cis-diamminedichloroplatinum(II)).

The section on platinum, like the others, is ingeneral well illustrated with line diagrams of chem-ical structures, and gives a good coverage of newdevelopments, such as active trans complexes andpotent di- and tri-Pt anticancer complexes, such asBBR3464. Not quite so good are some of the(grayscale) views of structures of DNA, proteinsand their adducts, e.g. Figures 10 and 11 inChapter 4. There is an omission concerning anintriguing feature of the structure of the adductbetween guanine-guanine platinated DNA and theprotein HMG1A, which is the intercalation of aprotein phenylalanine side chain between the plati-nated guanine bases on DNA. Such an adductprobably plays a crucial role in the mechanism ofaction of cisplatin. But this feature is not shown inthe picture on page 254; Figure 1 of this reviewshows an alternative view (1).

Diagnostic ImagingIt is a tribute to clever coordination chemistry

that gram quantities of potentially toxic gado-linium ions can be safely injected into a patientundergoing an MRI scan, in fact into millions ofpatients each year. The Gd3+ ion binds strongly tomultidentate chelated ligands, while still havingsufficient room in its coordination sphere to bindand relax water. Much elegant research is beingundertaken to optimise this effect: investigatingthe choice of the ligand donors, the size of the

21Platinum Metals Rev., 2008, 52, (1), 21–22

“Medicinal Applications of CoordinationChemistry”BY CHRIS J. JONES (University of Birmingham and The University of Manchester, U.K.) AND JOHN R. THORNBACK (MassTag

Technologies Ltd., U.K.), Royal Society of Chemistry, Cambridge, U.K., 2007, xii + 354 pages, ISBN 978-0-85404-596-9, £89.95,

U.S.$169.00

Reviewed by Peter J. SadlerDepartment of Chemistry, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, U.K.; E-mail: [email protected]

DOI: 10.1595/147106708X259497

complex, control of rotation, water exchangerates, targeting and so on. These features are welldescribed in thirty pages of Chapter 3, which alsodeals with radiopharmaceuticals, another area ofmuch commercial interest. Much attention isdeservedly focused on 99mTc, the short-lived (6 hhalf-life) technetium isotope-of-choice for manydiagnostic imaging procedures, with its wide rangeof oxidation states and potential for being targetedwith the right choice of ligands.

Other MetalsCoverage of other precious metals includes

gold, ruthenium (currently two complexes in clinical anticancer trials), palladium (much morekinetically labile than platinum, currently the subject of research) and rhodium (anticancerpotential). Surprisingly, silver is not dealt with,even though it is a very effective antibacterialagent. Washing machines containing slow-releasesilver are even being sold these days, to steriliseclothes as you wash them (see Samsung’sSilverCare Washing Machine!). Gold drugs have

been used for the treatment of difficult cases ofrheumatoid arthritis for over seventy years: gold istransported by albumin in the blood by binding tothe thiol at cysteine-34. This is depicted in Figure18 on page 288, but in fact the thiol group is par-tially buried in a crevice and not totally exposed onthe surface of the protein as the figure suggests.

Other topics covered include chelation therapy(for iron in thalassaemia, copper in Wilson’sdisease), vanadium as an insulin mimetic andsuperoxide dismutase mimics. A final chapter ondesign emphasises the need to control both thethermodynamics and kinetics of the reactions ofmetal complexes in biological (physiological)systems, in order to make real progress in thisfield. I missed bismuth (antiulcer drugs), antimony(antiparasitic) and arsenic (mentioned in passing,now a first-line treatment for certain typesof leukaemia). Three elements with poor NMRnuclei! Missing too, except as a passing men-tion, is lithium for treatment of bipolar disorder(taken by more than 1 in every 1000 of theU.K. population).

Concluding RemarksIt is fortunate that the authors included a dis-

claimer on page vii that their information must notbe relied upon to guide clinical decisions, since itsays on page 11 that Phase I clinical trials involve‘healthy volunteers’. This is not usually the casewith anticancer drugs, many of which are knownto be cytotoxic. For these, Phase I (which is main-ly concerned with establishing a safe dose foradministration) involves patients who have notresponded to other treatments.

This book will serve a useful role in teachinginorganic chemistry to both undergraduate andpostgraduate students. The topic helps to ‘bringinorganic chemistry to life’, and in my experiencedoes arouse their curiosity at all levels. It will be auseful addition to libraries, or if you shop aroundon the web, perhaps affordable for your ownpersonal bookshelves.

Reference1 U.-M. Ohndorf, M. A. Rould, Q. He, C. O. Pabo

and S. J. Lippard, Nature, 1999, 399, (6737), 708


Fig. 1 The insertion (intercalation) of phenylalanine-37side-chain (grey) from the HMG protein into thehydrophobic lesion on DNA created by a cisplatinintrastrand crosslink between two adjacent guanine bases(based on the Protein Data Bank (PDB) entry 1ckt (1)). Colour key: Yellow = platinum; Dark blue = N of NH3;Red helices = HMG protein; DNA bases: Green =guanine, G; Purple = cytosine, C; Red = adenine, A;Cyan = thymine, T

23

Light-Duty RegulatoryDevelopments

Although regulatory initiatives for dieseltailpipe emissions have already been establishedfor the foreseeable future in Japan and the U.S.,the EU is still in the process of finalising thetechnical details of the light-duty regulations forthe next 10 years. Concerning carbon dioxideemissions, the EU and automotive manufactur-ers came to a voluntary agreement a few yearsago. California finalised similar regulations in2005, which are currently undergoing judicialreview.

At the time of writing this review, theEuropean Union had approved the Euro V(2009) and Euro VI (2014) regulations. Figure 1shows how the control requirements of the new

proposed NOx regulations compare with thosein the U.S., not taking into account test cycle dif-ferences (within the range 10 to 20%). Alsoshown in Figure 1 are the approximate NOxreductions that would be required in order forEuro V- and Euro VI-compliant vehicles to besold in the U.S. The requirements of theJapanese 2009 regulations are similar to those ofEuro VI.

It is expected that compliance with the Euro V NOx regulations will largely be possiblewithout resort to NOx aftertreatment (1), butsignificant NOx controls will be needed if Euro V-compliant vehicles are to be saleable inall 50 states of the U.S. It is more likely thatEuro VI-compliant vehicles will be devel-oped in 2009/10, leveraging early incentive

Diesel Engine Emissions and Their ControlAN OVERVIEW

By Tim JohnsonCorning Environmental Technologies, Corning Incorporated, HP-CB-2-4, Corning, NY 14831, U.S.A.;

E-mail: [email protected]

This review covers recent developments in regulations to limit diesel emissions, enginetechnology, and remediation of nitrogen oxides (NOx) and particulate matter (PM). Thegeographical focus of regulatory development is now the European Union (EU), whereEuro V and Euro VI regulations for light-duty engines have been finalised for implementationin 2009 and 2014, respectively. The regulations are much more loosely drawn than those forthe U.S., but options exist for adapting European vehicles to the U.S. market. Europe is justbeginning to address heavy-duty regulations for 2013 and beyond. Engine technology is makingvery impressive progress, with clean combustion strategies in active development, mainlyfor U.S. light-duty application. Work with heavy-duty research engines is more focused ontraditional approaches, and will provide numerous engine/aftertreatment options for complyingwith the stringent U.S. 2010 regulations. NOx control is focusing on selective catalytic reduction(SCR) for diverse applications. Zeolite catalysts will be the mainstay of this technology forJapan and the U.S., and perhaps even for some Euro V-compliant applications. The emphasesare on low-temperature operation, secondary emissions and system optimisation. Lean NOxtraps (LNTs) are effective up to about 60 to 70% deNOx efficiency, and are being consideredfor light-duty applications. There is growing interest in supplementing LNT performance withintegrated SCR, which utilises ammonia generated in the LNT during rich regenerations.Diesel particulate filter (DPF) technology is at a stage of optimisation and cost reduction.Very sophisticated management strategies are being utilised, which open up options for theuse of new filter materials and alternative system architectures. Issues with secondary emissionsare emerging and are being addressed.


DOI: 10.1595/147106708X248750

programmes. Some NOx aftertreatment will berequired within that timeframe on the largervehicles. Either LNT or SCR will need to beapplied to the lighter vehicles to achieve the 60to 65% NOx reduction required for sales to allthe states in the U.S. Indeed, some Europeanmanufacturers have announced the introductionof Bin 5-compliant diesels for the U.S. in thistimeframe using these two NOx controltechnologies.

The European Commission is consideringadjusting the PM limit from 5 to 3 mg km–1 toreflect a new measurement protocol, and isdetermining an appropriate number-based PMemission limit (in number of particles per km).The technical protocol for this is being devel-oped and is close to approval. Testing andmonitoring of Euro V-compliant vehicles forparticulate number is being considered. Germanmanufacturers have agreed to use diesel particu-late filters on all cars by 2009.

Figure 2 shows how the European market isfaring in terms of carbon dioxide (CO2) emis-sions (2). In the light of increasing vehicle sizeand capacity, and a consumer desire for morepower, the targets were missed for the first timein 2005, and the trend does not look favourable.As a result, the European Commission and

Council of Ministers are formally consideringmandatory CO2 limit values. California’s regula-tions are mandatory and similar in restriction,but lag behind the European commitment bythree to four years.

To meet the CO2 targets, Thom (2) showedthat significant effort will be needed concerninggasoline vehicles heavier than about 1000 kg andon diesel vehicles heavier than about 1500 kg.

Apart from the CO2 targets, there are marketand political pressures on the auto companies toimprove fuel economy. The combination ofmore stringent tailpipe emission regulations andnecessary improvements in fuel economy isdriving significant technological progress inthe industry.

Heavy-Duty RegulatoryDevelopments

On the heavy-duty front, the picture is simi-lar. Japan and the U.S. have finalised theirregulations for the next five to ten years, butEurope is just beginning the process. In thatregard, the European Commission recentlyasked key stakeholders to comment on six regu-latory scenarios for the Euro VI standard in thetimeframe 2012 to 2014, ranging from no orminor tightening from Euro V to full adoption


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Fig. 1 Euro V and Euro VI light-duty NOx regulatory limits compared to the U.S.: (a) About 55 to 60% NOx controlwill be needed for a Euro V (2009) diesel to hit the U.S. Bin 8 maximum allowable emission (45 states). For Bin 5 (50states) nominally 85 to 90% NOx control is needed; (b) For Euro VI (2014), the requirement is 65 to 70% additionalNOx reduction

25

of U.S. 2010-type regulations with nominal lim-its of 0.20 g kWh–1 NOx and 0.010 g kWh–1 PM.For reference, the U.S. 2010 limits will be at 0.26g kWh–1 NOx and 0.013 g kWh–1 PM, and theJapanese 2009 limits are 0.7 g kWh–1 NOx and0.010 g kWh–1 PM. However, each has a differ-ent transient test cycle from Europe. To helpaddress that disparity, the EuropeanCommission adopted a new World HarmonisedTransient Cycle (WHTC), one that uses a higherload and speed than the Japanese cycle, but aspeed only slightly lower than for the currentEuropean Transient Cycle. Also under seriousconsideration are a number-based particulatestandard and a heavier in-use compliance mea-sure. The Commission aims to have a formalproposal ready for the Parliament by early 2008.

Light-Duty Engine DevelopmentsRegulatory, market, and fuel economy

requirements are making great demands ondiesel engine technology. Further, advancedgasoline concepts and hybrid electric vehiclesare exerting competitive technology pressures.Diesel engine developers are responding by

using advanced fuel injection technologies,exhaust gas recirculation (EGR) control,advanced and two-stage turbocharging, variablevalve actuation, closed-loop combustion con-trol, and advanced model-based control.Advanced diesel engines (3) are now approach-ing a specific power output of 70 kW l–1 and abrake mean effective pressure (BMEP) of 24bar. Some of these developments are allowingdiesel engines to approach Euro VI-compliantengine-out emissions levels (4, 5).

More sophisticated engine technologiescould lead to the adoption of economical light-duty diesels in the U.S. The fundamentalcharacteristics of these – the ‘advanced combus-tion, mixed mode’ engines – are illustrated inFigure 3 (6, 7).

In early injection strategies, much of the fuelcharge is mixed with gas before ignition. Thishelps to avoid the conditions for soot forma-tion. The NOx formation regime is avoided withhigh levels of EGR that keep the flame cooler.

With late injection strategies, the charge ismixed and simultaneously burned using, forexample, high swirl. The combination of good


KAMA average JAMA average

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Fig. 2 Progress towards meeting the EU voluntary CO2 limits (2). ACEA = European Automobile ManufacturersAssociation; JAMA = Japan Automobile Manufacturers Association; KAMA = Korea Automobile ManufacturersAssociation (Courtesy of DaimlerChrysler)


mixing and high EGR helps the charge avoidsoot and NOx formation regimes.

Managing these strategies becomes very diffi-cult as the amount of charge increases.Therefore, they are limited today to the lower-left-hand quadrant of the engine’s load-speedcharacteristic, up to perhaps 30 to 50% load andperhaps 50% speed. Traditional diesel combus-tion strategies will still be used at higher load,hence the term ‘mixed mode’. Low-loadadvanced combustion operation might be suffi-cient, as most of the points of the certificationtest cycle fall within this region. This minimisesthe amount of NOx aftertreatment that might berequired to meet the regulation, and probablyresults in cost savings. Indeed, some authors areprojecting that, for a properly designed vehicle,it might be possible to meet the U.S. 50-stateNOx requirements with no NOx aftertreatmentby the end of the decade (4). Even so, someNOx treatment will still be used to prevent ‘off-cycle’ emissions.

Heavy-Duty Engine DevelopmentsHeavy-duty (HD) diesel engine developments

are primarily aimed at improved fuel economy,reliability, cost and durability. As such, advancestend to be conservative and incremental. The

U.S. 2004 regulations were generally addressedusing advanced EGR and turbocharging mea-sures. U.S. 2007 and Japanese 2005 technologiesadded diesel particulate filters, whereas Euro IV(2005) and now Euro V (2008) regulations arelargely addressed by using more conventionalengine technologies and SCR.

Moving on to Japanese 2009 and U.S. 2010requirements, incremental advances on the earli-er compliant technologies will be seen.However, as with light-duty engines, advancedcombustion strategies may emerge to addresslow-load emissions issues. Because most of thefuel in heavy-duty applications is spent underhigher load regimes, engine researchers arefocusing more on traditional diesel combustionhardware and strategies, and they are making sig-nificant progress.

Figure 4 summarises results for high-loademissions from research engines (8–12) withrespect to the U.S. 2010 Not-to-Exceed (NTE)in-use emissions limits. U.S. NTE is the mostdifficult standard to meet under high load condi-tions in many applications. Figure 4 illustratesthe range of possibilities for HD engines using‘cutting edge’ hardware and control underlaboratory conditions. These results are cited asrepresenting the best results that technology

25%

20%

15%

10%5%1%

Sootformation

5000 ppm

NOx

500 ppm

Slow CO oxidation Rapid CO oxidation

15%O2

21% O2

10%O2

Lateinjection

Earlyinjection

6

5

4

3

2

1

0

Flam

e eq

uiva

lenc

e ra

tio

600 1000 1400 1800 2200 2600 3000Flame temperature, K

Fig. 3 Principles ofadvanced combustion (6)(Courtesy of SandiaNational Laboratory).Regimes of soot and NOxformation expressed interms of flameequivalence ratio(fuel:air ratio) and flametemperature. Soot andNOx are inhibited usinghigh exhaust gasrecirculation (EGR) levelswith either early (highlypremixed) fuel injectionor late injection. COoxidation zones fromReference (7)


might deliver in the next five years. With 75 to80% NOx control from SCR systems under highload conditions, allowable engine-out NOxemissions of 1.6 to 2.0 g kWh–1 (without engi-neering margin) are commensurate with PMemissions at about 0.025 to 0.050 g kWh–1, plac-ing PM NTE requirements well within thecapability of filters.

In the U.S., 2007 engines were required tomeet NOx NTE limits of about 2.3 g kWh–1.Without improvements, these engines needabout 85% NOx control to meet the U.S. 2010NTE requirements. With 90% efficient filters,meeting NTE PM limits is not a problem. A typ-ical 2007 high load point would be well off thegraph in Figure 4. It is reasonable to believe thatactual 2010 engines may incorporate nominal20% incremental improvements in engine-outNOx abatement relative to 2007 technology.

NOx Control TechnologiesSCR is emerging as a key NOx control strat-

egy for both light-duty and heavy-dutyapplications. It was first commercially availablein 2005 for European and Japanese HD applica-tions. The high NOx removal efficiency androbust performance of SCR allow fuel sensitiveapplications to be run at maximum efficiency(high engine-out NOx, low PM).

SCR is expected to be used in many 2010U.S. HD applications. In addition, several light-duty Tier 2 Bin 5 (50-state) applications have

been announced. For successful application ofSCR in the U.S., the Environmental ProtectionAgency (EPA) requires a plentiful, readily avail-able supply of urea, and that vehicle drivers keepurea on board. The key stakeholders in theindustry and the EPA developed a frameworkthat is incorporated in EPA guidelines (13).

On the light-duty side, the urea strategy(‘Bluetec II’) proposed by DaimlerChrysler (nowDaimler) and licensed to Volkswagen and BMWrequires that enough urea be kept on board toallow for filling at lubrication oil changes. This isperhaps up to 28 litres, assuming a 2% con-sumption rate relative to fuel for an 11,000 mile(17,600 km) range, according to Jackson et al.(14). The authors estimate that about half ofU.S. drivers would utilise lubrication shops forthis service. They also anticipate that 5- to 18-litre bottles of urea will also be available atfuelling stations and retail outlets at a cost ofU.S.$5.30 to U.S.$4.30 per litre, respectively.

On the heavy-duty side, a 1% urea consump-tion rate is expected. A 75-litre tank might last13,000 to 17,000 miles (21,000 to 27,000 km) forClass 8 and Class 6-7 vehicles respectively. TheClass 8 vehicles would need one urea fillbetween major services (i.e. lubrication oilchanges), whereas the smaller classes will not.Approximately 5000 truck stops pump abouthalf the on-road fuel. These vendors would use3000- to 15,000-litre urea stillages in the earlyyears, until urea demand reaches about 9500

0.050

0.040

0.030

0.020

0.010

Par

ticul

ate

mat

ter,

g kW

h–1

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6NOx, g kWh–1

U.S.NTElimits

Full load(8)

Full load(10)

Full load(11)

90% load(9)

Only NOx values werereported. PM rangesare estimates

C100 point(12), low PMcalibration

C100 point(12), low fuelconsumptioncalibration

Fig. 4 High load test steady-state test results on heavy-dutyresearch engines relative tothe challenging U.S. Not-to-Exceed (NTE) in-useregulatory requirement (8–12)


litres per month. After that point, undergroundtanks become more economic.

European SCR catalysts are based on vanadia,whereas those in Japan are zeolite-based. Giventhat zeolites have better high-temperature dura-bility, and that the SCR will be receiving very hotgas from the upstream filter system duringregenerations, zeolites are expected also to beused in the U.S. As Figure 5 shows, the new zeo-lite formulations perform better at the extremetemperatures and are less sensitive to non-idealNO2/NOx ratios (15).

SCR work is now being directed towardimproving low-temperature performance viamore accurate NO2/NOx control (a 50% ratioprovides the fastest reduction reaction), min-imising secondary emissions, and improvingon-board urea delivery systems. Given improv-

ing catalyst and system performance, low-tem-perature SCR systems are becoming viable aturea decomposition temperatures. If urea can bethermally decomposed, for example with abypass heater, system efficiency can beimproved from 75 to 95% (16). Slip catalysts aregenerally thought to remove most of the sec-ondary emissions from SCR systems, such asammonia, isocyanic acid (originating fromincomplete urea decomposition), nitrous oxideand nitrohydrocarbons (17). New slip catalystsare emerging that will convert ammonia all theway to nitrogen, and will probably abate hydro-carbon-based emissions as well (18). On-boardurea systems are now largely of the airlesstype (19, 20). Modelling of the urea-exhaust wallinteraction demonstrates enhanced mass andheat transfer for better urea distribution when

100

90

80

70

60

50

40

30

20

10

0

NO

x co

nver

sion

, %

100 150 200 250 300 350 400 450 500 550Temperature, ºC

Catalyst ACatalyst BV-SCR

(a)

100

80

60

40

20

0

NO

x co

nver

sion

, %

Catalyst A

Catalyst B

V-SCR

0 20 40 60 80 100[NO2]/[NO + NO2], %

(b)

Fig. 5 Performance ofzeolite selective catalyticreduction (SCR) catalysts(‘Catalyst A’ and ‘CatalystB’) relative to a standardwash coated vanadiacatalyst (V-SCR). Zeolitesexhibit: (a) better low temperatureand high temperatureperformance; and (b) less sensitivity to NO2

inlet levels (15)(Temperature = 200ºC)(Courtesy of JohnsonMatthey)


the spray is impinged on the pipe; however, thinfilms can form if the pipe temperature is lessthan about 280ºC (21). There is also much inter-est in urea systems affording a higher capacityby employing solid urea or magnesium chloride(MgCl2) as the storage medium. Solid urea lastsmore than twice as long as liquid urea for a givenvolume, but needs to be heated to about 180 to200ºC in the presence of water vapour todecompose to ammonia (22). MgCl2 storesammonia, and cartridges can readily be handled,replaced, recharged and recycled (23). It also hasthree times the volume-specific ammonia capac-ity and half the weight of Adblue®.Theoretically, a 28-litre tank will last 150,000miles (240,000 km) of testing under the FederalTest Procedure (FTP) when abating the emis-sion from a Bin 8-compliant light-duty engine toa Bin 5 tailpipe limit.

SCR is not always the preferred NOx abate-ment technology. Some vehicle manufacturersconsider that their customers will resist urea-SCR if other options exist. Also, mainly becauseof the relatively fixed cost of an on-board ureasystem, small LNTs are cheaper for engines ofless than about 2.0 to 2.5 litres capacity (24).Finally, since mixed-mode engines greatlyreduce low-load NOx, allowing LNT deploy-ment to focus on NOx entering at temperaturesgreater than about 300ºC, about 70% of theplatinum group metals (pgms) might beremoved (25). This could make LNT more eco-nomically attractive than SCR for cars withengines of up to 5 or 6 litres capacity (24, 26).

The durability of LNTs under sulfur contam-ination has always been a major problem. Thesulfur is removed by passing a rich, hot stream(700ºC) for a total of about 10 minutes every3000 to 6000 miles (5000 to 10,000 km).Although earlier LNTs lost perhaps 50% oftheir capacity over 15 to 20 desulfation cycles,newer versions now lose only about 25% of thefresh NOx capacity. Further, in the past it wasdifficult to control desulfation temperature towithin 700 to 800ºC. Newer control strategiesnow allow this degree of control (27), and per-haps even better. Given this, LNTs are effective

to about 60 to 70% NOx efficiency in ‘real-world’ light-duty systems (28), as shown inFigure 6. This is sufficient to bring a Euro V-compliant engine to Bin 8 compliance, or a EuroVI-compliant engine to Bin 5 compliance, asshown in Figure 1.

For the medium- and heavy-duty applica-tions, high-temperature LNT formulations arebeing developed to address the challenge ofmeeting the difficult high-load requirements ofthe U.S. NTE regulation (29). As LNTs need aperiodically rich stream to regenerate NOx andto desulfate, minimising the amount of rich gasused in the LNT saves fuel and helps control. Assuch, bypassing most of the lean exhaust pastthe LNT (29) or into an adjacent LNT system(30) can deliver good NOx reductions at reason-able fuel penalties – 75 to 80% efficiency at fullload, at 1.2 to 2.0% fuel penalty, with an LNTsized at 1.4 times the swept volume of theengine (swept volume ratio (SVR)). Theseresults, however, do not reflect deteriorationdue to significant ageing.

Finally, there has been much recent interestin combining LNTs with SCR. In this case, adownstream SCR catalyst stores ammonia that isgenerated in the LNT during rich operation. Theammonia can react with slipped rich NOx orlean NOx, increasing system efficiency, ordecreasing pgm loading, and hence cost at con-stant efficiency. A recent variant of this method

100

80

60

40

20

0

NO

x co

nver

sion

, %

100 200 300 400 500 600Temperature, ºC

Fig. 6 NOx performance curves for heavily-agedpotassium- and barium-based lean NOx traps (LNTs).U.S. Federal Test Procedure (FTP) efficiency is 63%.Swept volume ratio (SVR) = 0.94; 3.9 g l–1 pgm loading(28) (Courtesy of SAE and Umicore)

KBa


employs a NOx adsorber/SCR double layer con-figuration (31). Figure 7 shows the concept. Thesystem exhibits excellent low-temperature NOxconversion in the 200ºC range, but poor high-temperature conversion over 350ºC. Anotherfeature is that desulfation occurs at 500ºC, ascompared with 700 to 750ºC for conventionalLNT systems.

Particulate Matter ControlTechnologies

Platinum-based diesel particulate filters(DPFs) are now as integral to the diesel engineas fuel injectors. Within a couple of years, virtu-ally all new diesel cars in Europe, the U.S. andJapan will deploy DPFs. They have a high pene-tration in new Japanese trucks, and all new U.S.truck engines have used them since January2007.

Peugeot opened up this field with theannouncement of their system in April 1999, anda subsequent literature report (32). The systemcomprised a flexible common rail fuel injectionsystem, enabling late or post injections of hydro-carbons into a platinum-based diesel oxidationcatalyst (DOC) for burning to start DPF regen-eration, a cerium-based fuel-borne catalyst(FBC) to help burn the soot, and an uncatalysedsilicon carbide (SiC) DPF. In subsequent devel-opment, other automotive manufacturers chose

to catalyse the filter instead of using FBC, and inthe latest variant the DOC function is incorpo-rated into the filter (33). For medium-dutyapplications, approaches are similar to those forlight duty, but for the larger engines in the U.S.,auxiliary injectors or burners are deployed in theexhaust to impart DPF regeneration. Concernsin this regard are oil dilution by fuel from lateinjections, and the desire to decouple DPFinjection events from engine managementrequirements.

DPF management is becoming quite sophisti-cated. A platinum-catalysed filter system will‘passively’ regenerate from the reaction of NO2

with carbon under medium- and high-load con-ditions (34). Passive regeneration is limited bytemperature and by NOx:C ratios. Successfullong-term passive operation of filter systems(35) has been achieved with exhaust gas temper-ature profiles of 40% > 210ºC and NOx:sootratios less than 15. In extended operating condi-tions under which passive regeneration is notenough to keep the filter clean, ‘active’ regener-ation is needed. Zink et al. (36) reviewed theapproaches in the European light-duty sector,and identified common features:– Estimation of DPF soot loading using engine

and back pressure models, and fuel consump-tion;

– Preheating the system to ensure that injected

Lean (NOx adsorption) Rich (NH3 production& adsorption)

Lean (NH3-SCR, NOxadsorption)

4NH3(ad.)+2NOx+(3–x)O2→ 3N2 +6H2O

NO→NO(ad.)2NO+O2 →2NO2(ad.)

NO→NO(ad.)2NO+O2→2NO2(ad.)

NOx, O2

NH3 → NH3(ad.)

Reductant (CO, H2)

NH3

CO+H2O→ H2 +CO2

3H2 +2NOx(ad.)→2NH3 +xO2

NOx, O2

Solid acid

Pt/OSC

(Top)

(Bottom)

Fig. 7 In the NOx adsorber/selective catalytic reduction (SCR) combination double layer system, lean NOx is adsorbedon a ceria material. During rich operation some of the NOx is converted to ammonia which is stored and used duringlean operation on an upper platinum SCR catalyst (31) (Courtesy of ika and VKA Aachen Kolloquium; and Honda);OSC = oxygen storage capacity; ad. = adsorbed


hydrocarbons can ignite and heat up thefilter;

– Increase of exhaust hydrocarbon levels via in-cylinder or supplemental fuel injection, forburning on a catalyst;

– Control and monitoring of the regenerationas a function of operating point and con-ditions;

– Recalculation of pertinent models to takeaccount of ash build-up.Soot loading models have been in develop-

ment for many years. Although contemporarypressure-drop models take account of filter andcatalyst architecture, ash loading, PM character-istics, and completeness and nature ofregeneration, they still generally serve as supple-mentary algorithms to soot loadingdeterminations based on engine operatingconditions.

If active regeneration is required, a catalysttemperature in the range of 220 to 250ºC is nec-essary to burn injected hydrocarbons,sometimes calling for active system heat-upstrategies. Common approaches are air intakeand/or exhaust throttling, as well as appropriatelate injection of fuel (37). These measures enableheat-up at ambient temperatures of –10ºC with,in a medium-duty vehicle application, an averagespeed of 14 km h–1. The use of increasedelectrical loads on the engine has also beendescribed (38).

Once hot, fuel injection strategies will

depend on operating conditions (34, 38); seeFigure 8. To prevent lubricating oil ash fromsintering to itself, and to protect the DPF cata-lyst, soot burning exotherms need to becontrolled within suitable maxima. Some para-meters required for achieving this are filterthermal mass and catalyst loading, exhaust tem-perature and flow rate, and soot loading andcharacteristics. Craig et al. (39) provide an excel-lent example of how, under worst-case‘drop-to-idle’ (DTI) conditions (start soot com-bustion at high temperature and flow, and thendrop to idle), maximum exothermic tempera-tures vary with soot load, and gas temperatureand flow rate using cordierite filters. Karkkainenet al. (40) show how this information can beincorporated into a safe regeneration strategy, inwhich exhaust temperature is graduallyincreased from 550 to 600ºC as soot burns, andif the engine drops to idle, engine speed isincreased to remove heat from the filter.Additionally, managing oxygen through EGRcontrol is being proposed (1).

An example of the level of sophistication ofDPF soot loading models is offered byMuramatsu et al. (41). They found that the pri-mary soot combustion characteristics, namelyignition temperature and oxidation rate, dependon how the soot was generated. They quantifiedthese parameters and incorporated them intotheir control and monitoring model, part ofwhich is illustrated in Figure 9.

500

400

300

200

100

Torq

ue, N

m

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000Engine speed, RPM

Fig. 8 Different fuel injectionand throttling strategies areused to initiate and controldiesel particulate filter (DPF)regeneration (38) (The insetboxes show the general fuelinjection pattern (fuel quantityas a function of crank angle.)The colours represent theregimes on the engine mapwhere these injection patternsare operative. The dotted linedbox represents the operatingregime within which intakethrottling is used to increaseexhaust temperature.)


Advances in material science are likewisefacilitating developments in filter materials. Forlight-duty applications, SiC filters have been thestandard. However, aluminium titanate (AT) (33)filters are now in series production, and, aidedby better engine controls, the industry is begin-ning to move to the deployment of advancedcordierite (42) filters. Cordierite is the preferredfilter material for heavy-duty applications.

The properties of the new AT filters areimpressive in comparison with SiC materials.

The low thermal expansion and high strength ofAT mean that filter integrity is maintained with-out pasting smaller segments together to relievethermal shock in a larger filter. No cracks in thefilter material were observed even after a longrun of severe regeneration cycles (withexotherms to 1150ºC) (33). Further, tight con-trol of pore size reduces back pressure forcatalysed AT filters with soot, as shown inFigure 10.

Filter designers are also using cell geometry

Bac

k pr

essu

re, Δ

p, m

bar a

t 200

ºC

250

200

150

100

50

0 100 200 300 400 500Exhaust flow rate, m3 h–1

SiC 42% 200/14

SiC 42% 200/14

SiC 59% 300/12

SiC 59% 300/12

AT 300/13

DuraTrap®

AT 300/136 g l–1

0 g l–1

1 g l–1 min–1

Boundary

Same PMcombustion rate

constant

2 g–1 l–1

Spec

ific

parti

cula

teac

cum

ulat

ion,

g l–1

Normal combustionAbnormal combustion

500 550 600 650 700 750 800Inlet temperature, ºC

Fig. 10 Soot-loaded catalysed advanced aluminium titanate (AT) filters have 30% lower back pressure thancomparable SiC filters (33) (Courtesy of Technical University Dresden and Volkswagen AG)

Fig. 9 Relationship betweenfilter soot load and exhausttemperature to impart a normalregeneration event. Theboundary changes depend onsoot characteristics (41)(Courtesy of SAE)


creatively to increase ash storage capacity. Byincreasing the size of the inlet cell relative tothat of the exit cell, ash loading can increase by50% while maintaining the same back pressurefor soot-loaded filters; this is illustrated inFigure 11 (43).

Filter catalyst technology is advancingimpressively. Recent reports show that pgmloadings may be reduced and performanceimproved if the DOC function is incorporatedinto the filter via new coating methods. Filterregeneration is more complete as comparedwith systems with a separate DOC or FBC(44). In addition, hydrocarbon and CO reduc-tions are comparable to those with DOCsystems, and NO2 emissions are reduced (45).

As filter technology evolves and expands,more attention is being paid to secondaryemissions. In some European cities, ambientNO2 levels are increasing despite reduced orconstant total NOx levels. Much of thisincrease is attributable to the large numbers oflight-duty diesels that utilise DOCs (46), butsome evidence suggests that catalysed filtersystems are also contributors (47). Indeed, by2009 California will require that diesel retrofit

systems emit no more than 25% of the NOx asNO2. In that regard, Goersmann et al. (48)demonstrated a new system (Figure 12) thatabates more than 95% of the NO2 emissionscoming from catalysed DPFs.

Aerosol nanoparticles are another formof secondary emission under discussion.Epidemiological studies have correlated ad-verse health effects to particulate mass, andsome physiological evidence suggests thatsolid ultrafines can cause biological effects. Inthis regard, filter systems remove over 90% ofPM mass and over 99.9% of carbon and othersolid ultrafine particles. Some operating condi-tions (mainly high load and/or low ambienttemperature) may increase the emission ofaerosol nanoparticles in the < 30 nm sizerange from catalysed filter systems (49).Although the nanoparticles are almost all sul-fates, the use of ultra-low sulfur fuel and lowsulfur lubricating oil has only a minimal effect.However, when a sulfur trap is applied afterthe catalysed DPF system (50), the concentra-tion of aerosol ultrafine particles drops belowambient levels (49). Figure 13 shows someresults.

10

8

6

4

2

Bac

k pr

essu

re, Δ

p, k

Pa

at ro

omte

mpe

ratu

re a

nd 2

5 m

3h–1

0 10 20 30 40 50 60 70Ash load, g l–1

Std

Std

Std

10 g l–1 soot

5 g l–1 soot

0 g l–1 soot

ACT

ACT

ACT

Fig. 11 Asymmetric cell technology (ACT), wherein inlet diesel particulate filter (DPF) cells are largerthan exit cells, can give 50% more ash capacity while maintaining back pressure (43) (Courtesy of ikaand VKA Aachen Kolloquium; and Corning Incorporated)


Integrated NOx/ParticulateMatter Systems

The first integrated NOx and PM systems areexpected to enter service in 2008 in the U.S.

light-duty market and in 2009 in the Japaneseheavy-duty market, formally three months aheadof the U.S. 2010 heavy-duty market.

It is greatly preferable to position the NOx

2 Particulate filterPM (C) trapped[C] + 2NO2 → CO2 + 2NO

1 Oxidation catalystCO + ½O2 → CO2

[HC] + O2 → CO2 + H2ONO + ½O2 → NO2

3 NO2 decomposition catalyst[HC] + xNO2 → CO2 + H2O + xNO

Diesel fuel

CO

HC

PM

NOx

CO2

H2O

NO

Fig. 12 A new NO2 remediation system reduces 95% of the NO2 emissions from catalysed filtersystems (48) (Courtesy of Technical University Dresden and Johnson Matthey)

108

107

106

105

104

Aver

age

conc

entra

tion,

par

ticle

s cm

–3

200 220 240 260 280 300 320 340 360 380Average exhaust temperature, ºC

Average daily backgroundconcentration

CR-DPFNo sulfur trap

CR-DPFWith sulfur trap

Fig. 13 Sulfur-based aerosol ultrafine particulates can be generated in catalysedfilter systems. Sulfur traps reduce these emissions to below ambient levels (49). (CR-DPF = continuously regenerating diesel particulate filter) (Courtesy of SAE andUniversity of Minnesota)


system after the filter system to allow as muchpassive NO2-based regeneration of the filter aspossible. Using only active regenerations for thefilter can result in a net fuel penalty of up to 3%,depending on the drive cycle. However, forchassis-certified light-duty applications, fastlight-off of the NOx system is critical, so locat-ing the NOx system in front is being consideredfor those applications (51). For most heavy-dutyapplications, in which passive filter regenera-tions dominate and low fuel consumption iscritical, NOx systems are located behind thefilter.

Management of integrated NOx/PM systemspresents a unique set of challenges and syner-gies. For LNT-based systems, there aresynergies, such as coordinating desulfation withactive DPF regenerations, and utilising the peri-odic rich LNT regenerations to burn soot oncatalysed DPFs that contain oxygen storagewashcoats. For both SCR and LNT systems, theupstream DPF may provide NO2 to facilitate thedeNOx reactions. On the liability side, activeDPF regeneration could send hot gas into theNOx system, raising durability concerns. Also,management of the fuel injection for DPF orLNT management and urea injection steps ismore difficult.

Moving into the future, we expect to seeinnovative component and system integration,with plenty of choice between engine, DOC, fil-ter and deNOx options.

Recommendations for FutureWork

As the automotive industry progresses withadvanced combustion mixed-mode engines,especially in the light-duty sector, cold-starthydrocarbon and CO emissions in advancedmode, and/or NOx emissions in traditionalcombustion mode will become critical. Light-offshould be at temperatures lower than 175ºC.Further development is needed in the LNT andSCR systems, especially on the mechanisms ofammonia formation on LNT materials when runin the rich mode. Zeolite SCR catalysts also needimprovement to their performance in the low-temperature regimes, and better models areneeded to understand ammonia storage dynam-ics. Low-temperature (< 200ºC) urea decom-position is a limiting factor for many systems,and advanced hydrolysis catalysts might helphere. Lean NOx catalysts, using fuel instead ofammonia for the SCR reaction, show promisefor providing effective, low-cost NOx reduction.Much more work is needed on these catalystsystems.

For PM control, limiting NO2 emissions iscritical; here mathematical modelling, better cat-alysts and improved management methods areall needed. A better understanding of the cata-lyst-support-soot-gas interaction might lead tomore effective DPF catalysts.

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20 M. Parche, ‘Injection System and Engine Strategies forAdvanced Emission Standards’, SAE Heavy Duty

Diesel Emissions Control Symposium, Gothenburg,Sweden, September, 2005

21 F. Birkhold et al., ‘Analysis of the Injection of Urea-Water-Solution for Automotive SCR DeNOx-Systems:Modelling of Two-Phase Flow and Spray/WallInteraction’, SAE Technical Paper 2006-01-0643, SAE2006 World Congress & Exhibition, Detroit, MI,U.S.A., April, 2006

22 W. Mueller, ‘SCR Using Solid Urea’, 3rd InternationalExhaust Gas and Particulate Emissions Forum,Sinsheim, Germany, 14th–15th September, 2004

23 T. Johannessen, ‘Safe and Compact AmmoniaStorage/Delivery Systems for SCR-DeNOx inAutomotive Units’, U.S. Dept. of Energy 2006 DieselEngine-Efficiency and Emissions Research (DEER)Conference, Detroit, MI, U.S.A., 20th–24th August,2006

24 T. V. Johnson, ‘Diesel Emission Control in Review’,U.S. Dept. of Energy 2006 Diesel Engine-Efficiencyand Emissions Research (DEER) Conference, Detroit,MI, U.S.A., 20th–24th August, 2006

25 J. R. Theis et al., ‘The Effects of Aging Temperatureand PGM Loading on the NOx Storage Capacity of aLean NOx Trap’, SAE Technical Paper 2005-01-1117,SAE 2005 World Congress & Exhibition, Detroit, MI,U.S.A., April, 2005

26 J. Stang, ‘Cummins Light Truck Clean Diesel Engine’,U.S. Dept. of Energy 2004 Diesel Engine EmissionsReduction (DEER) Conference, Coronado, California,U.S.A., 29th August–2nd September, 2004

27 M.-C. Wu, ‘Experimental Evaluation of Reformate-Assisted Diesel NOx Trap Desulfation’, SAETechnical Paper 2005-01-3878, Powertrain & FluidSystems Conference & Exhibition, San Antonio, TX,U.S.A., October, 2005

28 F. Rohr, ‘NOx-Storage Catalyst Systems Designed toComply with North American Emission Legislationfor Diesel Passenger Cars’, SAE Technical Paper 2006-01-1369, SAE 2006 World Congress & Exhibition,Detroit, MI, U.S.A., April, 2006

29 A. Hinz et al., ‘The Application of a NOx AbsorberCatalyst System on a Heavy-Duty Diesel Engine’, SAETechnical Paper 2005-01-1084, SAE 2005 WorldCongress & Exhibition, Detroit, MI, U.S.A., April,2005

30 I. Tsumagari et al., ‘Study of 2-LEG NOx Storage-Reduction Catalyst System for HD Diesel Engine’,SAE Technical Paper 2006-01-0211, SAE 2006 WorldCongress & Exhibition, Detroit, MI, U.S.A., April,2006

31 N. Satoh et al., ‘A NOx Reduction System UsingAmmonia Storage-Selective Catalytic Reduction inRich and Lean Operations’, 15th Aachen Colloquium,Aachen, Germany, 10th–11th October, 2006

32 O. Salvat et al., ‘Passenger Car Serial Application of aParticulate Filter System on a Common-Rail, Direct-Injection Diesel Engine’, SAE Technical Paper2000-01-0473, SAE 2000 World Congress &Exhibition, Detroit, MI, U.S.A., March, 2000

33 R. Dorenkamp et al., ‘Application of a New FilterMaterial in Volkswagen’s Diesel Particulate FilterSystem’, Dresden Conference “Emission Control


The AuthorTim Johnson is Director – Emerging Regulations and Technologies for Corning EnvironmentalTechnologies, Corning Incorporated. Dr Johnson is responsible for tracking emerging mobile emissionsregulations and technologies, and helps develop strategic positioning via new products. He has been withCorning for twenty years, with ten years in the current position. He frequently speaks on diesel emissioncontrol technology and trends. In that regard, he received the 2007 Lloyd L. Withrow DistinguishedSpeaker Award from the SAE. Dr Johnson is a member of the U.S. Environmental Protection Agency (EPA)Clean Air Act Advisory Committee, and the EPA Mobile Sources Technical Review Subcommittee. He is alsoa member of the Northeast States Center for a Clean Air Future (NESCCAF/NESCAUM) board of directors,and he is on the Board of Advisors for the Center of Environmental Research and Technology at theUniversity of California, Riverside. He is also Co-Chairman of the Diesel Emission Control Committee at the

Manufacturers of Emission Controls Association (MECA). He was most recently the co-chair for the U.S. EPA’s Advisory Working Groupon Clean Diesel and Retrofit. He also served on the U.S. EPA Clean Diesel Independent Review Panel, and California Air ResourcesBoard International Diesel Retrofit Advisory Committee. Finally, he recently edited the book, “Diesel Particulate Filter Technology”,published by the SAE. Dr Johnson earned his BS and MS Engineering Degrees from the University of Minnesota in 1978 and 1979respectively, and his Doctor of Science from the Massachusetts Institute of Technology in 1987.

2006”, Technical University, Dresden, Germany,18th–19th May, 2006

34 G. Boretto et al., ‘Serial Application of a CatalyzedParticulate Filter on Common Rail DI Diesel Enginesfor Passenger Cars’, Paper no. F2004V068, FISITA2004 World Automotive Congress, Barcelona, Spain,23rd–27th May, 2004

35 T. L. Alleman et al., ‘Fuel Property, Emission Test, andOperability Results From a Fleet of Class 6 VehiclesOperating on Gas-To-Liquid Fuel and CatalyzedDiesel Particle Filters’, SAE Technical Paper 2004-01-2959, 2004 Powertrain & Fluid Systems Conference &Exhibition, Tampa, FL, U.S.A., October, 2004

36 U. H. Zink and T. V. Johnson, ‘State-of-the-Art FilterRegeneration Management – Concepts Realized byLDV Companies’, U.S. Dept. of Energy Diesel EngineEmissions Reduction (DEER) Conference, Chicago,IL, U.S.A., 21st–25th August, 2005

37 K. Komada et al., ‘Development of DPF System forCommercial Vehicles: (Second Report) – ActiveRegenerating Function in Various Driving Condition’,SAE Technical Paper 2005-01-3694, Powertrain &Fluid Systems Conference & Exhibition, San Antonio,TX, U.S.A., October, 2005

38 U. Plewnia, ‘Experiences with the Use of DieselParticulate Filters by OEMs as Standard Equipment’,Car Training Institute Forum “Exhaust Systems”,Ludwigsburg, Germany, 1st–2nd February, 2006

39 A. Craig et al., ‘Performance Aspects of CordieriteDiesel Particulate Filters in HD Applications’, SAE2005 Commercial Vehicle Engineering Congress &Exhibition, Chicago, IL, U.S.A., 1st–3rd November,2005

40 A. Karkkainen et al., ‘ Development and Application ofa US-EPA’07 Particulate Filter System for a 7.6LMedium Duty Truck Engine’, 15th AachenColloquium, Aachen, Germany, 10th–11th October,2006

41 T. Muramatsu et al., ‘DPR with Empirical Formula toImprove Active Regeneration of a PM Filter’, SAETechnical Paper 2006-01-0878, SAE 2006 WorldCongress & Exhibition, Detroit, MI, U.S.A., April,2006

42 ‘Corning Introduces Next-Generation Cordierite Filterfor Light-Duty Diesel Vehicles’, Corning Incorporated,

press release, New York, U.S.A., 27th April, 200643 A. Heibel et al., ‘Performance and Durability Evaluation

of the New Corning DuraTrap® AT Diesel ParticulateFilter – Results from Engine Bench and Vehicle Tests’,14th Aachen Colloquium, Aachen, Germany, 5th–6thOctober, 2005

44 M. Pfeifer et al., ‘The Second Generation of CatalyzedDiesel Particulate Filter Systems for Passenger Cars –Particulate Filters With Integrated Oxidation CatalystFunction’, SAE Technical Paper 2005-01-1756, SAE2005 World Congress & Exhibition, Detroit, MI,U.S.A., April, 2005

45 A. Punke et al., ‘Catalyzed Soot Filters in Close-CoupledPosition for Passenger Vehicles’, SAE Technical Paper2006-01-1091, SAE 2006 World Congress &Exhibition, Detroit, MI, U.S.A., April, 2006

46 R. Gense et al., ‘Latest Insights into Direct NO2

Emissions from Road Transport, the Current State ofKnowledge’, 2nd Conference Environment &Transport, Reims, France, 12th–14th June, 2006

47 U. Lambrecht et al., ‘High NO2-Concentrations inUrban Areas of Germany – The Influence of TrafficEmissions and Atmospheric Chemistry’, 2ndConference Environment & Transport, Reims, France,12th–14th June, 2006

48 C. Goersmann et al., ‘PM Control Systems with LowNO2 Emissions’, Dresden Conference ‘EmissionControl 2006’, Technical University, Dresden,Germany, 18th–19th May, 2006

49 D. Kittelson et al., ‘Driving Down On-HighwayParticulate Emissions’, SAE Technical Paper 2006-01-0916, SAE 2006 World Congress & Exhibition,Detroit, MI, U.S.A., April, 2006

50 A. Sawant, ‘On-Road Demonstration of UltrafineParticle Control Using Continuously RegeneratingDiesel Particulate Filters’, South Coast Air QualityManagement District “Ultrafine Particles: The Science,Technology and Policy Issues”, Los Angeles, CA,U.S.A., 30th April–2nd May, 2006

51 C. Lambert, ‘Urea SCR and DPF System for a Tier 2Diesel Light-Duty Truck’, U.S. Dept. of Energy 2006Diesel Engine-Efficiency and Emissions Research(DEER) Conference, Detroit, MI, U.S.A., 20th–24thAugust, 2006

38

The father of palladium-catalysed couplingchemistry is generally considered to be ProfessorRichard Heck. Although other reports onorganometallic coupling reactions had alreadybeen published, it was through his work that thePd-catalysed reactions became widely known andapplied. His initial publication of Pd-catalysedvinylic substitution reactions with aryl halidesappeared in 1972 (1), the year following the publi-cation of the same conversion, though underdifferent conditions, by Mizoroki (2). Heck’s in-itial choice of catalyst was Pd(II) acetate, althoughhe noted that Pd/C catalysts were also active,albeit that the reactions were slower and the yieldswere lower. His conclusion that “in spite of somelimitations, the organic halide–olefinic substitu-tion reaction should prove to be a useful syntheticreaction” has been entirely justified by history.

From this point on, throughout the 1970s fur-ther examples of Pd catalysis of C–C cross-coupling reactions continued to appear. The relat-ed coupling of aryl halides and alkynes rather thanalkenes was improved by Sonogashira using cop-per and Pd catalysts (3). The exploration of tinreagents in coupling chemistry is attributed toStille. A number of extremely useful transform-ations can be carried out using this chemistry (4).The coupling of aryl halides with organometallicderivatives of zinc and magnesium was firstreported by Negishi (5, 6) and Murahashi (7)

respectively (the latter now being commonlyreferred to as Kumada coupling due to priorpublications on the use of nickel catalysts for thisreaction). Pd competes with nickel catalysts forthese applications, and its preference must rely onimproved selectivity to overcome the costdisadvantages.

Although developed somewhat later than theHeck chemistry, the Suzuki-Miyaura reactionemploying boronic acids or esters has found readyacceptance by pharmaceutical chemists for thepreparation of biaryl derivatives. The basic re-action was initially published by Miyaura andSuzuki in 1979 (8, 9) using alkenyl boronates andalkenyl halides, but the ‘classic’ reaction of phenylboronic acid and aryl halides was reported in 1981(10). This chemistry has been greatly extended andelaborated over the years (11).

The original publications on Pd-catalysed cou-pling described the use of aryl bromides andiodides and for a number of years there were noeffective catalysts for most aryl chlorides. Thisrelates to the strength of the Ar–X bond, whichincreases: I < Br < Cl (65, 81 and 96 kcal mol–1

respectively) and makes the oxidative additionstep increasingly difficult (12). Aryl chlorides offersignificantly greater scope as substrates than dobromides or iodides, and at lower cost. The abil-ity to react these substrates has come aboutthrough an improved understanding of the


Palladium-Catalysed C–C Coupling:Then and NowBy Chris BarnardJohnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, U.K.; E-mail: [email protected]

Synthetic procedures for the manufacture of complex drug molecules have changed continuallyover the years as methodology has improved. However, a step change in efficiency has beenachieved by switching from a linear pattern of steps (often more than ten) to a different strategy:the parallel synthesis of key precursor components and then linking them together at a latestage in the process. This has only been possible due to the advances in coupling chemistrythat have occurred over the last thirty years, many of them related to the use of palladiumcatalysis. This article sets out to describe some of the early work in palladium-catalysed C–Cbond formation and how the methodologies have changed due to recent developments.

DOI: 10.1595/147106708X256634

mechanism and the ways to enhance the rate-determining step. Understanding the properties ofthe Pd intermediates in the catalytic cycle hasallowed the reactions to be applied to a widerrange of substrates with improved selectivityunder milder conditions.

The mechanism of the Heck reaction and therelated cross-couplings has been studied inten-sively over the years and an outline is shown inFigure 1 (13). The Pd species introduced as thecatalyst precursor is believed to be converted toan active species of low coordination numberallowing the oxidative addition of the aryl halide.The olefin then binds to a further vacant site onthe catalyst. Combination of the aryl and olefiniccomponents and β-hydride elimination forms theproduct and base-promoted reductive eliminationof HX regenerates the catalyst. There has beensome debate as to whether Pd(0)/Pd(II) orPd(II)/Pd(IV) forms the basis for the oxidative

addition/reductive elimination cycle (14–16), withthe former believed to be operative in the vastmajority of, if not all, cases. The use of stronglystabilising ligands (e.g. in palladacycles) may yieldcatalysts with very high turnover number (averagenumber of catalytic cycles per molecule of cata-lyst) and high reactivity, but generally only undervigorous conditions which are believed to beassociated with slow reduction/dissociation ofthe precursor complex (17). The coordination ofspectator ligands at Pd is also in question, and asa consequence the charge on the catalytic interme-diates may vary under different reactionconditions (16, 18) and the reaction can no longerbe adequately described by a simple mechanismsuch as that given in Figure 1 (12).

Industrial applications were reviewed byde Vries, who also highlighted the importance ofeconomic factors in defining the catalytic precur-sor (19). Ligandless systems are the most cost


LnPdsol

sol

LnPdX

Ar

LnPdX

LnPdAr'

Ar

ArAr'

ArX

Ar'MZ

R

ArCH=CHRLnPdX

H

R

Ar

LXPdAr

LL

R

Reductive Elimination

Hydrideelimination

Migratory insertion

Oxidativeaddition

Olef in binding

HECK COUPLINGCROSS COUPLING

XMZ

Transmetalation

ReductiveElimination

Pd0 or PdII

precursor

M = B, Si, Mg, Zn, Al, Zr

CROSS COUPLING HECK COUPLINGPd(0) or Pd(II)

precursor

Reductive elimination

Reductiveelimination

Oxidativeaddition

Migratory insertion

Olefin binding

Transmetallation

Hydrideelimination

XMZn

Ar′MZn

M = B, Si, Mg, Zn, Al, Zr

ArX

ArAr′

ArCH=CHR

L

R

X

ArLnPd

LnPd

LXPd LAr

RAr

RX

X

HLnPd

LnPd

LnPd

solv

solv

Ar′

Ar

Fig. 1 Outline of mechanisms of Heck and related cross-coupling reactions (L= ligand; solv = solvent; X, Z = halogen(Cl, Br or I))

efficient, but are active for only the more reactivesubstrates. The application of supported Pdcatalysts has continued to generate interest overthe years and the performance of these systemscan often be enhanced by the addition of phos-phines. This suggests that at least some of theactivity of these catalysts is due to leached molec-ular species. A detailed review considering thispoint has recently been published (17), and furthersupport for the role of leached Pd(0) species hasbeen provided by the work of Jones (20) andKöhler (21). The range of patented cross-couplingtechnologies has been reviewed by Corbet andMignani (22).

Regioselectivity in the Heck reaction can beachieved though control of the electronic proper-ties of the alkene. The reaction generally worksbest with electron-withdrawing substituents onthe alkene and gives the β-aryl substitutedproducts in high yield. For electron-donatingsubstituents the α-substituted product can beobtained in good yield under halide-free condi-tions. This is believed to be associated with shiftsin the mechanism related to the charge on the cat-alytic intermediates. Recently, some progress hasbeen made in regiocontrol of the reactions of arylhalides as well (23, 24). Some control of the cis andtrans stereochemistry of the product can also beachieved through the optimal choice of catalystand base.

While the mechanisms of all the Pd-catalysedcoupling reactions have much in common, theconditions for the cross-coupling reactions aregenerally milder than those for the Heck reactionand several groups have delighted in achieving thehighest turnovers for the reaction under themildest conditions. Buchwald et al. were first todescribe catalysts highly active at room temper-ature for aryl bromides (25). Subsequently, the cat-alysts have been further developed to allowcoupling of aryl chlorides under similarly mildconditions. The use of bulky, strongly electron-donating phosphines has been key to thesedevelopments, with many derivatives offeringsimilar performance with standard substrates.More recently, this chemistry has been extendedto the coupling of alkyl as well as aryl chlorides

(26), and with application to alkyl boranes(27, 28). Further developments are anticipated.

Heck ReactionsHeck initially noted that ethylene could be cou-

pled with an aryl group in a non-catalytic reactionusing the arylmercury halide in 1968. The catalyt-ic reaction of olefins such as styrene usingpalladium acetate (Pd(OAc)2) at 1 mol% relativeto the aryl halide was reported in 1972 (1). Foriodobenzene the reaction was completed by heat-ing at 100ºC for typically 1 to 5 hours, butbromobenzene was much less reactive.

Early work on using aryl chlorides revealed thatconventional catalytic systems (for examplePd(OAc)2/PPh3) were effective for electron-defi-cient substrates provided forcing conditions(150ºC) were used. Pd catalysts stable to theseconditions, such as palladacycle (15), pincer (29)and carbene (30) complexes were then shown tobe active. Bidentate phosphines, 1,2-bis(diphenyl-phosphino)ethane (dppe) or 1,4-bis(diisopropyl-phosphino)butane (dippb), have also been foundto be useful in these reactions, although their per-formance can be very sensitive to both thesubstituents on phosphorus and the length of thecarbon bridge (31). In 1999, Littke and Fu report-ed the Heck coupling of methyl acrylate or styrenewith a variety of unactivated aryl chlorides usingtri(tert-butyl)phosphine (P(tBu)3) as ligand (32),with a similar preference being found by Hartwigin a screening study (33). The initial Fu reportindicated the use of Cs2CO3 as base with reactiontemperatures of 100 to 120ºC, but milder condi-tions were possible when the base was changed toCy2NMe (34). Aryl bromides and activated, elec-tron-deficient aryl chlorides could now be reactedat room temperature. Also, the use of differentPd:P ratios suggested a monophosphine species asthe active catalyst. This catalyst system alsoproved to be versatile, allowing a wide choice ofelectron-rich and hindered aryl chlorides, and ofolefinic partners. It is noteworthy that the othertriaryl and trialkyl phosphines studied providedineffective catalysts.

In an industrial context, cost control is impor-tant and a variety of ligandless Pd systems have


been developed. As commented above, in his initialstudies Heck found Pd/C to have low activity, butin 1973 Julia et al. reported some activity for arylchlorides (35), and interest has revived in the lastten years. Extensive efforts have been made todevelop other supported Pd catalysts suitable forrecycle, involving both ligandless and anchored lig-and systems. Improved conditions have beendeveloped allowing high turnover numbers for arylbromides and reaction of unactivated aryl chlorides(21). This area of C–C coupling by heterogeneousPd catalysts has been reviewed recently (36).

Unsupported Pd nanoparticles can also be used(37), and a process whereby these particles are col-lected on an inexpensive carrier such as Celite® (apurified diatomaceous earth product), and thenreactivated by oxidation with iodine, has beendeveloped by DSM (19).

The use of alternative solvent media (for exam-ple, supercritical fluids or ionic liquids) andreaction conditions (such as microwaves or ultra-sound) to optimise the performance of the Heckreaction has also been reviewed (38).

Suzuki-Miyaura ReactionsInitial work on the coupling of alkenyl halides

with alkenyl boranes with tetrakis(triphenylphos-phine)palladium (Pd(PPh3)4) in 1979 identified thekey role of the base in achieving high yields (7, 8).In 1981 the ‘classic’ Suzuki-Miyaura reaction ofphenyl boronic acid with aryl halides was reported(9). Again, the preferred catalyst was Pd(PPh3)4

being used in benzene at reflux. In both these stud-ies aryl chlorides such as chlorobenzene were“quite inert”.

Suzuki-Miyaura coupling of activated aryl chlo-rides is possible with a wide range of catalysts asthese reactions proceed more readily than manyother cross-couplings. For example, chloropy-ridines can be coupled using the original Pd(PPh3)4

catalyst. In 1997 Shen reported the use of tricyclo-hexylphosphine (PCy3) for the coupling ofactivated aryl chlorides (39), and the following yearFu reported further work with PCy3 and P(tBu)3

establishing reactivity for a wider range of arylchlorides (40). Shen proposed that the PCy3 ligandmight promote oxidative addition of the aryl

chloride, and that its steric demands might facilitatethe formation of a monophosphine complex as theactive catalyst and promote reductive elimination.All of these arguments have been subsequentlyelaborated in further work to design alternative cat-alysts. Studies conducted on the optimum Pd:PR3

ratio for in situ preparation of the catalysts indicat-ed that this lies in the range 1 to 1.5 suggesting thata monophosphine complex is the most active cata-lyst (41). Hartwig studied the dimeric complexdi-μ-bromobis(tri-tert-butylphosphine)dipalladi-um(I) ([PdBr(P(tBu)3)]2) as a precursor suited to thegeneration of monophosphine species and deter-mined that it is a highly effective catalyst (42).Beller also studied a series of 1,6-diene palladi-um(0) monophosphine complexes, 1, and foundthem to be suitable for aryl chloride couplings (43).

Buchwald has developed a series of ligandsbased on a 2,2'-biphenyl motif (44, 45).Biphenyldialkylphosphine (alkyl = tbutyl or cyclo-hexyl) reacts with a variety of unactivated arylchlorides at room temperature with approximately1 mol% Pd. Further optimisation of these ligandshas allowed coupling of aryl, heteroaryl and vinylboronic acids with extremely hindered aryl chlo-rides and heteroaryl halides, with the ligand shownas structure 2, (R = Me) being particularly preferred(45). Interaction between the Pd and C(1) of thesecond (remote) biphenyl ring is believed to play akey role in the catalytic properties of this group of


PdCy3P O

Pd0 monophosphinecomplex

1 Monophosphine1,6-diene complex ofPd(0)

Cy3P Pd O

OR

PCy2

RO

Buchwald ligands2 Buchwald ligands

ORRO

PCy2

ligands. Fu also demonstrated that PCy3 catalystsare effective for the coupling of aryl and vinyl tri-flates, and even simple alkyl bromides andchlorides (albeit with catalyst loading of 10 mol%Pd) (27, 28). In further attempts to optimise thecombination of steric and electronic properties ofthe ligand, a number of other compounds havebeen introduced recently, e.g. mono- and bis-phos-phino ferrocenes (46, 47), methyl-di-t-butyl-phosphine (48), di(adamantyl)-n-butylphosphineand other di-adamantylphosphine ligands (49–52).

In developing a series of palladacyle complexes,Bedford found that the combination of PCy3 witha P,C-palladacycle of a phosphite ligand bearing asalicylate group, 3, showed exceptional longevityand hence could be used at very low loadings (53).Guram, Buchwald and Fu have all reported recent-ly on Suzuki-Miyaura coupling of derivatives ofnitrogen heterocycles (chlorides or boronic acids)(54–56).

The recent interest in N-heterocyclic carbenes(NHCs) as alternatives to phosphine ligands hasincluded applications in coupling (57). These lig-ands are strong electron donors and carry bulkysubstituents so they might be expected to activatearyl chloride substrates. This has been borne outby a number of examples, in the work of Nolan, inparticular. Imidazolium salts such as IMes HCl andIPr HCl, 4, provide an air-stable source of precur-sor carbene complex when reacted in situ withPd2dba3 (dba = dibenzylideneacetone) leading tosimplified and more effective experimental proce-dures. With approximately 2 mol% catalyst goodyields were obtained with many aryl chlorides andtriflates (30).

Stille ReactionsThe synthesis of ketones from acid chlorides and

organotin compounds using Pd catalysis was reportedby Stille in 1978 (58). The scope and versatility ofthis chemistry was demonstrated by the mid-1980s(4), although its industrial application has been limitedby concerns over tin residues in the product andwaste streams. Catalysts employed in the early workon aryl bromides, iodides and triflates includedbenzyl(chloro)bis(triphenylphosphine)palladium(PdCl(CH2Ph)(PPh3)2) and Pd(PPh3)4. Further workdemonstrated the advantages of tris-2-furylphosphineor triphenylarsine ligands in this chemistry (59). Stillecoupling has been widely studied in reactions ofheteroaryl chlorides but there are fewer exampleswith aryl chlorides. For unactivated aryl chloridesit has been found that P(tBu)3 yields suitable systems(60). The complex bis(tri-tert-butylphosphine)-palladium (Pd(P(tBu)3)2) can also be used as catalystat loadings down to 0.1 mol% Pd. The combinationof Pd(OAc)2 and the imidazolium salt IPr HCl, 4, inthe presence of nBu4NF was also effective forcoupling aryl bromides and electron-deficient arylchlorides (61), while Bedford et al. reported thatsimple Pd precursors with PCy3 gave very effectivecatalysis (62).

Hiyama ReactionsThe reaction with organosilanes is more recent-

ly developed than the other cross-couplings,suitable conditions being identified by Hiyama in1988 (63, 64). The preferred catalyst wasbis(allyl)dichlorodipalladium ([PdCl(η3-C3H5)]2) at2.5 mol% under mild conditions, ambient to 50ºCgiving acceptable yields with aryl iodides and bro-mides (65). The reaction was extended to selectedaryl chlorides in 1996 with the adoption of


O

O OPO

Pd PCy3

Cl

Palladacycle complex

tBu

tBu

3 Palladacycle complex

PCy3

t Bu

t Bu PO

O

O O

P

Cl

N N

IPr imidazolium salt(carbene precursor)

Cl

4 IPr imidazolium salt(carbene precursor)

NN

Cl

dichlorobis(triisopropylphosphine)palladium(PdCl2(P(iPr)3)2) as catalyst in the presence of KF(66). Fluoride-free reactions of aryl halides (Br andCl) with aryl and vinyl siloxanes have beenachieved through the use of concentrated aqueoussodium hydroxide (50%) at 120ºC, with tetrabutyl-ammonium bromide being used as an additive insome cases (67, 68).

Negishi ReactionsAlthough he studied the coupling of a range of

organometallic derivatives (aluminium, magnesium,zinc and zirconium), the name of Negishi isassociated with cross-coupling using organozincderivatives, as reported in 1977 using PdCl2(PPh3)2

plus iBu2AlH to generate the Pd(0) catalyst (5, 6).The reactions of heteroaryl chlorides were widelystudied using a variety of Pd(0) and Pd(II) catalysts.The first general method applicable to aryl chlorideswas developed in 2001 by Fu using as catalystPd(P(tBu)3)2 at 2 mol% and 100ºC with 1:1THF/NMP as solvent (69). Hindered compoundsreacted satisfactorily and up to 3000 turnovers wereachieved. Buchwald extended his series ofbiphenyldialkylphosphine ligands to include anexample – 2,6-di-isopropoxy-substituted – (see 2)which gave excellent results in a wide variety ofNegishi couplings (70). Pd/dppf-based (dppf =diphenylphosphinoferrocene) catalysts have alsobeen found to be useful in this class of reactions (71).

Kumada ReactionsAlthough the metal-catalysed coupling (particu-

larly Ni and Pd) with organomagnesium reagents(Grignards) has been studied for some time, theapplicability of these reactions is limited due to thehigh reactivity of the Grignard reagents with avariety of functional groups. Early work usedPd(PPh3)4 (7, 72) as catalyst. Studies by Kumadaet al. of bidentate phosphines suggested that thebite angle is important and that the large value fordppf was particularly suitable – possibly due to theease of dissociation of one phosphorus donor(71). Initial work on activated aryl chlorides alsoused PdCl2(dppf) (effective down to 0.1 mol% cat-alyst in THF at 85ºC) (73). Other work describedthe use of palladacycles under more forcing condi-

tions (15) and more recently the application ofPd2(dba)3/NHCs has been described (74). Thepreferred ligand was IPr derived from the imida-zolium salt 4.

Sonogashira ReactionsAlthough the coupling of aryl halides and

alkynes had been reported previously, the condi-tions reported by Sonogashira in 1975 greatlyimproved the attractiveness of this reaction (3).This reaction is often used to convert heteroarylchlorides to fused-ring heterocycles. The combi-nation of Pd catalyst (typically PdCl2(PPh3)2) withcopper iodide and amine base allowed the cou-pling to be carried out at room temperature in sixhours. It is believed that copper assists the reac-tion through formation of an acetylide and thenthis group is transferred to Pd by a transmetalla-tion step. However, the formation of copperacetylides can also lead to homocoupling products,so modification of the conditions, and in particu-lar copper-free conditions, have continued to beinvestigated. In contrast to many of the reactionsabove, although different researchers have estab-lished some flexibility in the conditions, no generalmethod is yet available for all substrates for thisreaction. Aryl chlorides and tosylates can be cou-pled using PdCl2(PhCN)2 and a biphenyl-dicyclohexylphosphine under copper-free condi-tions (75) and the addition of tetrabutyl-ammonium fluoride to PdCl2(PPh3)2 allows a cop-per-, amine- and solvent-free alkynylation of arylhalides (76). A detailed review of the Sonogashirareaction has recently been published (77).

ConclusionFrom the early studies which exemplified these

reactions using catalysts based on simple Pdcompounds (chloride, acetate) and triphenyl-phosphine (for example, Pd(PPh3)4, PdCl2(PPh3)2)these reactions have been extended to cover the fullchoice of aryl halides with even sterically restrictedpartners. Changing from aryl to alkyl substituentson phosphorus has reduced the barrier to oxidativeaddition of the stronger aryl chloride bond and moresubtle interactions between the ligand and the Pdatom promote the migratory insertion/reductive



elimination of the products. Thus Fu and Hartwighave shown the wide applicability of PCy3 and P(tBu)3

systems, while Buchwald has demonstrated theextraordinary versatility of biphenyldialkylphosphineligands. Many other groups have demonstrated thathighly stable precursors such as palladacyle, pincer

and carbene complexes can generate highly activespecies. It is certain that the remarkable advances incoupling chemistry that have been made in academiclaboratories will be increasingly incorporated intoindustrial fine chemical and pharmaceuticalpreparations.

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68 E. Alacid and C. Nájera, Adv. Synth. Catal., 2006,348, (15), 2085

69 C. Dai and G. C. Fu, J. Am. Chem. Soc., 2001, 123,(12), 2719

70 J. E. Milne and S. L. Buchwald, J. Am. Chem. Soc.,2004, 126, (40), 13028

71 T. Hayashi, M. Konishi, Y. Kobori, M. Kumada, T.Higuchi and K. Hirotsu, J. Am. Chem. Soc., 1984, 106,(1), 158

72 S. Murahashi, M. Yamamura, K. Yanagisawa, N.Mita and K. Kondo, J. Org. Chem., 1979, 44, (14),2408

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74 J. Huang and S. P. Nolan, J. Am. Chem. Soc., 1999,121, (42), 9889

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77 R. Chinchilla and C. Nájera, Chem. Rev., 2007, 107,(3), 874

Further ReadingA. F. Littke and G. C. Fu, ‘Palladium-Catalyzed CouplingReactions of Aryl Chlorides’, Angew. Chem. Int. Ed., 2002,41, (22), 4176J. Tsuji, “Palladium Reagents and Catalysts: NewPerspectives for the 21st Century”, John Wiley and Sons,Ltd., Chichester, 2004“Metal-catalyzed Cross-coupling Reactions”, 2nd Edn.,eds. A. de Meijere and F. Diederich, Wiley-VCH,Weinheim, 2004V. Farina, V. Krishnamurthy and W. J. Scott, “The StilleReaction”, John Wiley and Sons, Inc., New York, 1998

The AuthorChris Barnard is a Scientific Consultant in theLiquid Phase Catalysis Group at the JohnsonMatthey Technology Centre, U.K., withinterests in homogeneous catalysisemploying the platinum group metals. He isalso interested in the application of platinumcompounds as cancer therapy.


This book surveys the wide range of currentresearch activities concerned with transitionmetallopolymer-based functional materials. Thereare thirteen chapters. The first chapter, by C. U.Pittman, Jr. and C. E. Carraher, Jr., is devoted to theearly stages of research and development ofmetallopolymers in the 1960s and 1970s. This isfollowed by twelve chapters addressing differentcategories of transition metal-containing polymers,dendrimers and biopolymer systems with regard totheir preparation, potential applications and futureprospects. Some of the chapters having relevance tothe platinum group metals (pgms) are highlighted inthis review.

Metal-Containing PolymericMaterials

Since the early 1990s, organometallic com-pounds have been at the forefront ofinterdisciplinary (science and engineering)research. Polymeric materials based on the bond-ing of metals to polymeric chains, their syntheticmethodologies, their properties as well as theirapplications are highlighted in the second chapter,entitled ‘Recent Developments in OrganometallicPolymers’, by A. S. Abd-El-Aziz and P. O.Shipman. This covers the diverse synthetic routesfor the preparation of transition metal-containingmacromolecules, and their chemical and physicalproperties. These metallopolymeric materials areclassified on the basis of the bonding of the metalsto the macromolecular chain: metallic moieties inthe polymer backbone, pendent to the polymerbackbone or in the side chains, and the orientationof the metallic counterpart in star structures, den-drimers and hyperbranched polymers. A widerange of transition metals, including platinum,

palladium, ruthenium and osmium, and other ele-ments (such as aluminium, silicon, tin and gold)serve as the metallic component in these kinds oforganometallic polymers. The unique electrical,optical, catalytic and magnetic properties of suchorganometallic polymers have attracted manyresearch groups around the world, as evidenced bythe more than 350 references given in this chapter.

Metal-containing block copolymers are one ofthe most active research areas in the metallopoly-mer field as a result of their properties and wealthof potential applications. Metallopolymers withprecisely controlled chain length, or with block,star, or dendritic architectures, are currentlyattracting much attention. The third chapter,‘Block Copolymers with Transition Metals in theMain Chain’, by D. A. Rider and I. Manners, cov-ers a wide range of block copolymers withmetallo-linkers, metal-centred star structures, andpolyferrocenylsilane (PFS)-based materials. Self-assembly of PFS block copolymers withsingle-walled carbon nanotubes could, for exam-ple, be used in high-throughput field-effecttransistors. This chapter discusses this and manyother such exciting possibilities for the develop-ment of new functional nanostructured materialsvia a self-assembly approach.

Integrating metals into the conjugated frame-work of a polymer can influence its electronic,optical and magnetic properties. The metal may actas an n- or p-dopant to alter the polymer’s conduc-tivity, provided that the metal and polymer areelectronically coupled. The fourth chapter, ‘Metal-Containing π-Conjugated Polymers’, by M. J.MacLachlan, covers the broad range of zinc(II)porphyrin systems. An excellent review of metal-containing polythiophene-based polymers has been

“Frontiers in Transition Metal-ContainingPolymers”EDITED BY ALAA S. ABD-EL-AZIZ (University of British Columbia Okanagan, Canada) and IAN MANNERS (University of Bristol,

U.K.), John Wiley & Sons, Inc., New Jersey, U.S.A., 2007, 533 pages, ISBN 978-0-471-73015-6, £71.50, €101.50

Reviewed by Kaushik MallickAdvanced Materials Division, Mintek, Private Bag X3015, Randburg 2125, South Africa; E-mail: [email protected]

DOI: 10.1595/147106708X256409

included in this chapter, in which ruthenium, palla-dium, osmium, iron, cobalt, nickel, copper, zincand gold have been incorporated as the metalliccounterpart in the polythiophene system.

The fabrication of well-defined nanosized pat-terns composed of organics, metals andsemiconductors has been one of the major chal-lenges to chemists, physicists and materialscientists alike. Such materials are showing greatpromise in various technological areas, such asphotonics, electronics, catalysis, sensing, energyconservation and biomedical applications. Metal-containing block copolymers are a novel class ofmaterials that have potential for wide applicationin nanofabrication. The fifth chapter, ‘MetalCoordination Polymers for Nanofabrication’, byW. K. Chan and K. W. Cheng, reviews a variety ofblock copolymers such as the derivatives of poly(2-vinylpyridine) and poly(4-vinylpyridine), porphy-rin-containing polymers and derivatives of poly-norborene. Platinum and palladium can beattached to methyltetracyclododecane (MTD) toform the complex-blocks [Pt]50[MTD]113,[Pd]50[MTD]113 and [Pd]10[MTD]163. Block copoly-mers offer an alternative approach to thefabrication of large areas of regular and orderedpatterns. They are thus potentially useful in thefabrication of new-generation molecular electronicdevices.

Luminescence and SensorsHighly branched macromolecular architecture

has become a key fundamental research area. Thetenth chapter, ‘Metallodendrimers and TheirPotential Utilitarian Applications’, by S.-H. Hwangand G. R. Newkome, discusses such unique com-pounds in terms of their luminescence and sensorproperties. Luminescence is an excited-state phe-nomenon and is used in laser, display and sensorapplications. The ruthenium-based dendritictetranuclear Ru(II) complex shows nonexponentialluminescence decay with a lifetime in the range10–5 to 10–8 s. Metallodendrimers consisting ofencapsulated palladium, platinum or iridium por-phyrins are used for the quantification of dissolvedmolecular oxygen. This chapter reviews a range ofexamples of the unique features of dendritic archi-

tecture, and the organotransition metal complexesthat have been combined in metallodendrimerscreating the potential for practical applications.

Other TopicsOther chapters discuss such topics as rigid-rod

polymetallaynes, polymers with metal–metal bondsalong their backbones, polypeptide-based metallo-biopolymers, supramolecular metal arrays onartificial metallo-DNAs and peptides, metalloden-dritic iron complexes, redox-based functionalitiesof multinuclear metal complex systems, and one-dimensional transition metal-containing coord-ination/organometallic polymers.

ConclusionsThe book covers many areas of current

research in the exciting and emerging fields oforganometallics, metal-polymer/dendrimer com-plex materials, metallo-biopolymers, and metallo-DNA and metallo-peptide supramolecular com-pounds. The book would interest scientists fromdiverse research areas associated with materials sci-ence as well as very specialised organometallic andorganic chemists.

Nanotechnology offers an extremely broadrange of potential applications in electronics, opti-cal communication and biological systems.Platinum group/transition metal ions andnanoparticles with different sizes and shapes,combined with organic molecules, can give rise tohost supramolecules with interesting physicalproperties and important potential applications.Such compounds are thoroughly discussed in thisbook on the basis of the techniques used for theirsynthesis and their properties. The challengesahead are detailed, as are the many present andpossible future applications and directions forsuch systems.

A prominent future for the pgms in this area iscertain. The editors state that the “book aims tosurvey recent research at the frontiers of the sub-ject”. Their aim is achieved. The book contains533 pages with the chapters quoting referencesdated typically up to 2005. It is an excellent collec-tion of research results and measured predictionsfor the future.


48

Work has been ongoing in building a thermo-dynamic database for the prediction of phaseequilibria in Pt-based superalloys (1–7). The alloys arebeing developed for high-temperature applications inaggressive environments. The database will aid thedesign of alloys by enabling the calculation of thecomposition and proportions of phases present inalloys of different compositions. This paper is arevised account of work presented at the conference:Southern African Institute of Mining and Metallurgy‘Platinum Surges Ahead’ at Sun City, South Africa,from 8th to 12th October 2006 (7).

Part I, describing initial results for the Pt-Al-Ru

system from the compound energy formalism model,was published in the July 2007 issue of Platinum MetalsReview (1). Part II (2) described the different approachwhich was needed for the other binary and ternarycombinations within the Pr-Al-Cr-Ru system, withsimpler representation to allow for sparse data. Thispaper (Part III) completes the series by outliningwork at the University of Bayreuth on the platinum-aluminium-chromium-nickel (Pt-Al-Cr-Ni) database,using thermodynamic calculations from first princi-ples (ab initio). The Pt-Al-Cr-Ni database is eventuallyto be merged with the Pt-Al-Cr-Ru database to give aPt-Al-Cr-Ni-Ru database.

Building a Thermodynamic Database forPlatinum-Based Superalloys: Part IIIRESULTS OF CALCULATIONS FROM FIRST PRINCIPLES

By J. Preußner*Metals and Alloys, Universität Bayreuth, Ludwig-Thoma-Straße 36b, D-95447 Bayreuth, Germany;

*E-mail: [email protected]

S. N. PrinsNational Metrology Institute of South Africa, Private Bag X34, Lynwood Ridge 0040, South Africa,

and Phases Research Lab, Department of Materials Science and Engineering, Pennsylvania State University, University Park,

PA 16802, U.S.A.

M. WenderothSiemens AG, Medical Solutions, Vacuum Technology Division, Röntgenstraße 2, D-07407 Rudolstadt, Germany

R. VölklMetals and Alloys, Universität Bayreuth, Ludwig-Thoma-Straße 36b, D-95447 Bayreuth, Germany

and U. Glatzel**Metals and Alloys, Universität Bayreuth, Ludwig-Thoma-Straße 36b, D-95447 Bayreuth, Germany;

**E-mail: [email protected]

Work is being done at Mintek, the University of Leeds and the University of Bayreuth tobuild up a platinum-aluminium-chromium-ruthenium (Pt-Al-Cr-Ru) database for the predictionof phase diagrams for further alloy development by obtaining good thermodynamic descriptionsof all of the possible phases in the system. Binary descriptions were combined, allowingextrapolation into the ternary systems, and experimental phase equilibrium data were comparedwith calculated results. Part I of this series of papers (1) addressed the Pt-Al-Ru system,and Part II (2) the Pt-Cr-Ru system. This final paper (Part III) deals with progress towardsa platinum-aluminium-chromium-nickel (Pt-Al-Cr-Ni) database at the University of Bayreuth,using thermodynamic calculations from first principles to deal with the problem of sparsedata. The Pt-Al-Cr-Ru and Pt-Al-Cr-Ni databases will eventually be merged to give a Pt-Al-Cr-Ni-Ru database.


DOI: 10.1595/147106708X255167


Calculations from First Principles(Ab Initio)

Part II of this series of papers (2) described asimplified approach to the calculation of phase dia-grams, for cases where use of the compound energyformalism model (1) is inappropriate due to thesparseness of experimental data.

At the University of Bayreuth, a differentapproach has been used to compensate for sparsedata, using ab initio calculations to determine theenthalpy of formation of intermetallic compounds.These calculations, which are complex and timeconsuming, are based on density functional theory,as described by Kohn and Sham (8). The power ofthe technique derives from the fact that the thermo-dynamic results are often difficult to determineexperimentally. The results can be used directly in athermodynamic description of the alloy systems (9).The VASP program (10) has been used here to cal-culate the enthalpies of formation of the orderedcompounds. At this stage, no magnetic contributionhas been incorporated in the calculations, sincethere is some discrepancy in the experimental obser-vations: for the L12-ordered CrPt3 Kussmann et al.(11) observed ferromagnetic behaviour, whereasPickard et al. (12) observed ferrimagnetic behaviour.The total enthalpies of the pure elements were com-pared with those obtained by Wang et al. (13), withvery good agreement.

Resulting Chromium-PlatinumPhase Diagram

The calculated phase diagram after thermo-dynamic optimisation is given in Figure 1 (7), andshows very good agreement with experimental data.The modelled eutectic temperatures agree, withinthe stated experimental errors, with the results ofVenkatraman and Neumann (14) (derived on thebasis of Massalski (15)), rather than those of Oikawaet al. (16). The ordering reaction still needs to bemodelled correctly, and a later version of the Cr-Ptphase diagram shows promise (17). The small phaseregion of the L12 CrPt3 phase at low temperaturesmay be a result of not yet having taken the mag-netic properties into account. Since all the Gibbsenergies have now been modelled, it is possible tocalculate further thermodynamic data. Figure 2shows a comparison between the calculated andexperimental chemical activities (18, 20). Using abinitio calculations in the thermodynamic model haspredicted the presence of L12 Cr3Pt at low tempera-tures. This suggests that the platinum-rich side ofthe phase diagram should be examined further,probably using the diagram from Zhao (17).

Platinum-Aluminium-Chromium-Nickel

Thermodynamic assessment of the Cr-Pt systemhas already shown that many regions of the binary

49

Tem

pera

ture

, K

2200

2000

1800

1600

1400

1200

1000

800

600

400

2000 0.2 0.4 0.6 0.8 1.0

Pt, mole fraction

b.c.c. f.c.c.

Liquid

A15

Ordered phases

Fig. 1 Cr-Pt phase diagramcalculated using ab initio values.Symbols denote experimental valuesfrom Reference (14) and referencestherein

50

phase diagram are relatively unknown. The ab initiocalculations used here show that a stable L12 Cr3Ptstructure is achieved. Greenfield and Beck (21) dis-covered a stable L12 structure at 63 at.% Cr,although it is not shown in experimental phase dia-grams (14). More experimental work using rigorousX-ray diffraction techniques needs to be done tosubstantiate the L12 and L10 phase regions. A data-base for the Pt-Al-Cr-Ni system will be created.Many experiments on the Pt-rich side of the Pt-Al-Cr-Ni system have already been performed (22).The addition of nickel increases the curvature of theγ' solvus, as shown in Figure 3 (23).

ConclusionsThe principal aim of the ongoing work at the

University of Bayreuth is to describe the platinum-rich side of the Pt-Al-Cr-Ni system. It has beendemonstrated that ab initio calculations can provide

helpful information on the formation of phases tocompensate for sparse experimental data on thealloy system. It is hoped that, in the long term, theBayreuth database can be merged with the Pt-Al-Cr-Ru database, which is being developed byMintek and the University of Leeds (see Part II ofthis series of papers (2)).

AcknowledgementsFinancial assistance from the South African

Department of Science and Technology (DST); thePlatinum Development Initiative (PDI: AngloPlatinum, Impala Platinum and Lonmin);DST/NRF Centre of Excellence in StrongMaterials; EPSRC Platform Grant GR/R95798;Deutsche Forschungsgemeinschaft (DFG; GermanResearch Foundation); and Japan Society for thePromotion of Science (JSPS) is gratefully acknowl-edged. This paper is published with the permissionof Mintek and the Southern African Institute ofMining and Metallurgy.


Act

ivity

ratio

1.00.90.80.70.60.50.40.30.20.1

00 0.2 0.4 0.6 0.8 1.0

Pt, mole fraction

Ref. (19)Ref. (20)

– Calculated

Fig. 2 Calculated activity of Cr and Pt at 1500°C (withrespect to the pure phases at 1500°C) compared withexperimental results (19, 20)

Pt

30 at.% Ni

30 at.% Al

γ′γ

Fig. 3 Phase diagram forthe Pt-rich side of the Pt-Al-Cr-Ni system; experimentalpoints (measured byWenderoth and Vorberg) aretaken from Reference (23).See Table I for key

Table I

Key to Figure 3 (EPMA = electron probe microanalyser; SEM-EDX = scanning electronmicroscopy-energy dispersive X-ray detection)

Symbol System Technique Remarks

Pt-Al-Cr-Ni SEM-EDX Firstexperimental series

Pt-Al-Cr-Ni SEM-EDX Secondexperimental series

PtAl12Ni6 EPMA –PtAl12Cr6 EPMA –PtAl12Cr6Ni5 SEM-EDX –

Δ Pt-Al-Cr-Ni SEM-EDX Furthermeasurements


1 L. A. Cornish, R. Süss, A. Watson and S. N. Prins,Platinum Metals Rev., 2007, 51, (3), 104

2 A. Watson, R. Süss and L. A. Cornish, Platinum MetalsRev., 2007, 51, (4), 189

3 I. M. Wolff and P. J. Hill, Platinum Metals Rev., 2000,44, (4), 158

4 L. A. Cornish, J. Hohls, P. J. Hill, S. Prins, R. Süssand D. N. Compton, J. Min. Metall. Sect. B: Metall.,2002, 38, (3–4), 197

5 L. A. Cornish, R. Süss, L. H. Chown, S. Taylor, L.Glaner, A. Douglas and S. N. Prins, ‘Platinum-BasedAlloys for High Temperature and SpecialApplications’, in “International Platinum Conference‘Platinum Adding Value’”, Sun City, South Africa,3rd–7th October, 2004, Symposium Series S38, TheSouth African Institute of Mining and Metallurgy,Johannesburg, South Africa, 2004, pp. 329–336

6 L. A. Cornish, R. Süss, A. Watson and S. N. Prins,‘Building a Database for the Prediction of Phases inPt-based Superalloys’, in “Second InternationalPlatinum Conference ‘Platinum Surges Ahead’”, SunCity, South Africa, 8th–12th October, 2006,Symposium Series S45, The Southern AfricanInstitute of Mining and Metallurgy, Johannesburg,South Africa, 2006, pp. 91–102; http://www.platinum.org.za/Pt2006/index.htm

7 J. Preussner, M. Wenderoth, S. N. Prins, R. Völkl andU. Glatzel, ‘Platinum Alloy Development – the Pt-Al-Cr-Ni System’, in “Second International PlatinumConference ‘Platinum Surges Ahead’”, Sun City,South Africa, 8th–12th October, 2006, SymposiumSeries S45, The Southern African Institute of Miningand Metallurgy, Johannesburg, South Africa, 2006,pp. 103–106; http://www.platinum.org.za/Pt2006/index.htm

8 W. Kohn and L. J. Sham, Phys. Rev., 1965, 140, (4A),A1133

9 C. Wolverton, X.-Y. Yan, R. Vijayaraghavan and V.

Ozolinš, Acta Mater., 2002, 50, (9), 218710 G. Kresse, “VASP, Vienna Ab-initio Package

Simulation”, Theoretical Physics Department,Vienna University, 2004; http://cms.mpi.univie.ac.at/vasp/

11 A. Kussmann, K. Müller and E. Raub, Z. Metallkd.,1968, 59, (11), 859

12 S. J. Pickart and R. Nathans, J. Appl. Phys., 1962, 33,(3), 1336

13 Y. Wang, S. Curtarolo, C. Jiang, R. Arroyave, T. Wang,G. Ceder, L.-Q. Chen and Z.-K. Liu, CALPHAD,2004, 28, (1), 79

14 M. Venkatraman and J. P. Neumann, Bull. Alloy PhaseDiag., 1990, 11, (1), 16

15 “Binary Alloy Phase Diagrams”, 2nd Edn., eds. T. B.Massalski, H. Okamoto, P. R. Subramanian and L.Kacprzak, in 3 volumes, ASM International, Ohio,U.S.A., 1990

16 K. Oikawa, G. W. Qin, T. Ikeshoja, O. Kitakami, Y.Shimada, K. Ishida and K. Fukamichi, J. Magn. Magn.Mater., 2001, 236, (1–2), 220

17 J.-C. Zhao, X. Zeng and D. G. Cahill, Mater. Today,2005, 8, (10), 28

18 R. M. Waterstrat, Metall. Trans., 1973, 4, (6), 158519 A. M. Garbers-Craig and R. J. Dippenaar, Metall.

Mater. Trans. B, 1997, 28, (4), 54720 D. A. R. Kay and A. K. Mohanty, Metall. Trans., 1970,

1, 30321 P. Greenfield and P. A. Beck, J. Met., 1956, 8, (AIME

Trans. 206), 26522 M. Wenderoth, L. A. Cornish, R. Süss, S. Vorberg, B.

Fischer, U. Glatzel and R. Völkl, Metall. Mater. Trans.A, 2005, 36, (3), 567

23 S. Vorberg, “Entwicklung von Platinbasis-Super-legierungen”, Ph.D. Thesis, Universität Bayreuth,Germany, Verlag Dr. Köster, Berlin, 2006,ISBN 978-3-89574-607-9

References

Johannes Preußner is ascientific researcher andPh.D. student at theChair of Metals andAlloys at the Universityof Bayreuth, Germany.His main interestsinclude modelling and

simulation in materials science and newhigh-temperature materials.

Sara Prins is a researchmetrologist at theNational MetrologyInstitute of South Africa.She is undertaking Ph.D.research at thePennsylvania StateUniversity, U.S.A., where

she is working on phase diagram andfirst-principles calculations.

Dr.-Ing. Rainer Völkl isan academic councillorand senior researcher atthe Chair of Metals andAlloys, University ofBayreuth. His main fieldsof research include alloysof platinum group metals

as well as nickel base alloys, testing ofmechanical properties at hightemperatures and electron microscopy.

In his Ph.D. thesis at the University of Bayreuth,Markus Wenderoth developed new precipitation-hardened platinum base alloys for application athigh temperatures and experimentally analysedtheir microstructure, high-temperature strengthand oxidation behaviour. He is now working as aproduction engineer with Siemens MedicalSolutions, Vacuum Technology Division.

Professor Dr.-Ing. Uwe Glatzel is head of theChair of Metals and Alloys at the University ofBayreuth. His work had a big impact on thedevelopment of modern high-temperaturealloys, mainly nickel base superalloys. Headvises several research groups, includingthose working on platinum-based superalloysand other alloys for high-temperatureapplications, laser metallurgy, material analysisand artificial knee joints.

The Authors

DOI: 10.1595/147106708X264158

This is the second book on platinum jewellerysmithing (see also (1)) from Jurgen Maerz,Director of Technical Education, Platinum GuildInternational USA and a certified MasterGoldsmith. It is also the latest in a series of practi-cal softback jewellery handbooks published byMJSA Press (2). Aimed at the practising bench jew-eller, this lavishly illustrated book is a compilationof a number of practical articles published in theMJSA Journal with some additional material.

Tricks of the TradeSubtitled “Tricks to Overcome a Jeweler’s Daily

Challenges”, Jurgen shares many of the tricks ofthe trade from his own extensive experience thatwill enable a jeweller to make platinum jewellerywithout too many tears. As well as his tricks andsome projects (I counted about thirty-nine in all),Jurgen also relates some tales of working at thebench and the pitfalls that have befallen him in thepast. This account serves as invaluable advice andhelps to make this book such an enjoyable read aswell as a useful tool. Jurgen’s bright personalityshines throughout the book from cover to cover.

Each trick or project that he describes teachesthe jeweller how to perform tasks through a seriesof step-by-step instructions, amply illustrated bycolour photographs taken at the bench. ‘A picturespeaks a thousand words’ goes the adage. In thiscase it is undoubtedly true. The projects are practi-cal approaches to aspects of platinum jewellerymanufacture and include topics as diverse as chan-nel setting, platinum chain manufacture andmaking a heart pendant. A number of techniquesinvolving the use of a laser are described, and thebook finishes with a useful section on benchresources, a series of advertisements for platinummaterials, services and equipment suppliers.

Work SmarterThis book will be very useful to both the novice

and seasoned jeweller alike. As that expert gold-smith and author, Alan Revere (3), says in hisIntroduction to the book, “Jurgen’s tricks willcause even the seasoned goldsmith to slap their(now balding) head and ask themselves, ‘Whydidn’t I think of that before?’”. I am sure that even


“Adventures at the Bench”BY JURGEN J. MAERZ (Platinum Guild International USA), MJSA Press, Providence, U.S.A., 2006, 112 pages,

ISBN 978-0-9713495-7-5, U.S.$34.95

Reviewed by Christopher CortiCOReGOLD Technology Consultancy, Reading, U.K.; E-mail: [email protected]

Jurgen Maerz

Making a platinumbracelet (Courtesy ofMJSA Press): (a) sawingthe flat links after windingthe wire on a mandrel; (b)soldering the round links;(c) polishing the assembledbracelet

(a) (b)

(c)


Alan found much to learn and enjoy from readingthis book. I certainly did, even though I am not apractising bench jeweller. It is a great tool to haveon the bench and I commend it to any bench jew-eller working with platinum.

As Alan says in his Introduction, “This book isfull of clever tips, shortcuts and homemade toolsto help jewellers work smarter, by being more effi-cient and economical”. I could not put it bettermyself. Those who know him personally will beaware that Jurgen’s hobby is performing magictricks in front of his friends and colleagues. He hascertainly conjured up some good ones here!Sponsored by Johnson Matthey NY, this book is afirst-class and unique addition to any bench jew-eller’s bookshelf and will provide muchinspiration, invaluable advice and considerableenjoyment.

References1 Jurgen J. Maerz, “The Platinum Bench”, MJSA

Press, Providence, U.S.A., 20022 Manufacturing Jewelers & Suppliers of America,

MJSA Press: http://www.mjsa.org/info_press.php3 Revere Academy of Jewelry Arts, San Francisco,

U.S.A.: http://www.revereacademy.com/

The ReviewerChristopher Corti holds a Ph.D. in Metallurgy fromthe University of Surrey, U.K., and is currently aconsultant for the World Gold Council and theWorshipful Company of Goldsmiths in London. Heserved as Editor of Gold Technology magazine andcurrently edits Gold Bulletin journal and theGoldsmiths’ Company Technical Bulletin. A recipientof the Santa Fe Symposium® Research Award,Technology Award and Ambassador Award, he is afrequent presenter at the Santa Fe Symposium® onJewelry Manufacturing Technology.

Using a clothes peg as a multipurpose vice to assemble apearl to its post (Courtesy of MJSA Press)


DOI: 10.1595/147106708X265670

Johnson Matthey’s latest market survey ofplatinum group metals (pgms) supply anddemand was published in November 2007, pro-viding detailed forecasts of pgm supply anddemand for the full calendar year, plus short-term market outlook and six-month platinumand palladium price predictions. The InterimReview updates information provided in the fullannual survey “Platinum 2007” (1).

Platinum2007 Market Deficit Forecast

Johnson Matthey forecast that annual globaldemand for platinum would rise by 195,000 oz,or 2.9 per cent, to a record 6.925 million oz in2007. Due to a challenging operating environ-ment, South African platinum supplies were notexpected to reach previously expected targets.Global platinum supplies, at 6.66 million oz,were forecast to be lower than in 2006 by135,000 oz, with the 2007 platinum markettherefore moving back from the small surplus in2006 to a deficit of 265,000 oz.

Supply Below ExpectationsGlobal platinum supply was predicted to drop

by 2.0 per cent to 6.66 million oz in 2007. Salesfrom South Africa were expected to fall by70,000 oz, to 5.22 million oz. Russian supplies,at 820,000 oz, were forecast to be in line withprimary production.

Increasing Autocatalyst DemandAutocatalyst demand was forecast to rise by

2.3 per cent to 4.235 million oz in 2007, withdemand boosted by an increase in the fitment ofplatinum-containing particulate filters to dieselcars, by rising aftertreatment requirements in theglobal heavy-duty diesel market, and by growthin Asian light-duty vehicle output. These factorswere cited as more than outweighing the effectsof reducing platinum catalyst loadings, the con-tinuing substitution of palladium for platinum ongasoline vehicles and further use of palladium indiesel autocatalysts.

Rising Industrial PurchasesIndustrial purchases of platinum were expect-

ed by Johnson Matthey to rise by 40,000 oz to1.91 million oz in 2007. Growth was noted inchemical, electrical and petroleum refining appli-cations, with the Chinese and Indian economiesan important driving force. Chemical sector pur-chases were expected to grow by 3.9 per cent to395,000 oz, due to rising global demand formany bulk chemicals which require platinum-based catalysts for their manufacture. Growingcomputer and IT equipment production wasforecast to increase platinum purchases by theelectronics industry to 435,000 oz, as hard diskshipments rose. Petroleum refining purchaseswere expected to rise to a total of 230,000 oz.Dental demand was predicted to fall due to pricesensitivity. Glass manufacturing demand was

Platinum 2007 Interim Review

Disappointing South African pgmoutput for 2007 was expected, dueto a combination of geological andsafety problems, industrial unrestand processing bottlenecks(Courtesy of Lonmin Plc)


also predicted to fall, due to a decline in newfacilities being built.

Jewellery Demand Little ChangedA slight fall in demand was predicted for new

metal from platinum jewellery manufacturers in2007, of 1.5 per cent to 1.595 million oz.Recycling was expected to satisfy a high propor-tion of manufacturing requirements in Japan andChina. Although in Japan demand was expectedto fall by 55,000 oz to 305,000 oz, growing con-sumer interest led to Chinese demand for newmetal being forecast to grow by 20,000 oz to780,000 oz in 2007.

PalladiumMarket to Remain in Surplus

Palladium demand was forecast to grow in2007, rising by 135,000 oz, or 2.1 per cent, to6.61 million oz. Autocatalyst demand was pre-dicted to increase due to strong growth in Asianvehicle manufacturing, and the use of palladiumto replace platinum in some catalysts. However,demand for new palladium for jewellery lookedset to drop by more than a quarter in 2007 aspurchases by manufacturers in China declined.Production of palladium would fall in SouthAfrica but supply from Russia was forecast torise in 2007. Supply was forecast as reaching 8.32million oz in 2007, with the market showinganother substantial surplus, of 1.715 million oz.

Strong Growth in Autocatalyst DemandJohnson Matthey expected purchases of palla-

dium by the automotive sector to rise by 340,000oz, or 8.4 per cent, to 4.38 million oz, a six yearhigh. In addition to rising production of palladi-um autocatalysts to supply the Asian vehiclemarket, demand was stimulated by the wide pricedifferential between palladium and platinum. Inthe gasoline sector, the use of palladium insteadof platinum catalysts continues to grow; roughlythree times as much palladium as platinum isnow used in gasoline cars. In light-duty dieselautocatalysts, the use of palladium was forecastto increase to over 200,000 oz in 2007, morethan double the figure for 2006.

Modest Rise in Industrial DemandJohnson Matthey predicted continued grow-

ing demand for palladium from the electronicssector, to 1.10 million oz, driven by growth inconsumer demand and in subsectors such asplating. Although little change in demand wasforecast from 2006, dental sector uptake hasbeen downgraded by Johnson Matthey to takeaccount of greater recycling than previouslythought.

Fall in New Metal Purchases for JewelleryGlobal demand for new palladium for jew-

ellery manufacturing was forecast as falling by250,000 oz to 745,000 oz in 2007. European andNorth American demand were expected to riseslightly as new ranges of jewellery are launched inthese regions. In the more established Chinesemarket, demand in 2007 was expected to dropfrom 760,000 oz to 500,000 oz, with demand fornew metal again being offset by recycling.

Availability of Interim Review“Platinum 2007 Interim Review” is available

free of charge in printed form from JohnsonMatthey PLC, Precious Metals Marketing,Orchard Road, Royston, Hertfordshire SG85HE, U.K.; E-mail: [email protected]. Thereport may also be freely downloaded in PDFformat from the website:http://www.platinum.matthey.com/.

Reference1 Platinum Metals Rev., 2007, 51, (3), 155

Palladium purchases for jewellery manufacture in2007 were expected to grow in Europe and NorthAmerica as more companies started to experimentwith this material (Courtesy of Mark B. Mann/MannDesign Group, Inc.)

CATALYSIS – APPLIED AND PHYSICAL ASPECTSQuantitative Analysis of Transient SurfaceReactions on Planar Catalyst with Time-ResolvedTime-of-Flight Mass SpectrometryK. OKUMURA, Y. SAKAMOTO, T. KAYAMA, Y. KIZAKI, H.SHINJOH and T. MOTOHIRO, Rev. Sci. Instrum., 2007, 78, (10),104102 (9 pages)

The title analysis employed pulsed-gas valves for theinjection of reactant molecules. The products of NO+ H2 reaction on a planar catalyst, Pt–Al2O3/Si sub-strates inserted into a micro tube reactor with SiCballs, were analysed. The procedure enabled analysisof the transient consecutive secondary catalytic reac-tions as well as primary reactions based on theformation rate of product molecules per millisecond.

Platinum Nanoparticles Supported on IonicLiquid-Modified Magnetic Nanoparticles:Selective Hydrogenation CatalystsR. ABU-REZIQ, D. WANG, M. POST and H. ALPER, Adv. Synth.Catal., 2007, 349, (13), 2145–2150

Pt nanoparticles were supported on magneticnanoparticles modified with ionic liquid groups, byadsorbing K2PtCl4 on the surface of magnetitenanoparticles via ion exchange with the linked ionicliquid groups, and then reducing using hydrazine. Theobtained catalyst (1) was used for the selective hydro-genation of alkynes and α,β-unsaturated aldehydes.(1) can be separated by an external magnetic field.

Characterization of Metal Segregation inPt–Re/Al2O3 Reforming CatalystsYU. V. GURYEV, I. I. IVANOVA, V. V. LUNIN, W. GRÜNERT andM. W. E. VAN DEN BERG, Appl. Catal. A: Gen., 2007, 329,16–21

Mono- and bimetallic Pt-Re catalysts (1) with 0.3 wt.%of each metal were investigated. The combination of H2

and O2 chemisorption techniques was demonstrated tobe a sensitive tool to monitor Pt-Re interaction. Thepresence of H2O on (1) during high-temperature treat-ments was a major factor affecting Pt and Reaggregation and segregation.

Role of Gas-Phase Chemistry in the RichCombustion of H2 and CO over a Rh/Al2O3 Catalystin Annular ReactorM. MAESTRI, A. BERETTA, T. FARAVELLI, G. GROPPI and E.TRONCONI, Chem. Eng. Sci., 2007, 62, (18–20), 4992–4997

A 2D isothermal model was used to analyse H2- andCO-rich combustions over Rh/Al2O3. As foundexperimentally, homogeneous ignition of H2/O2 waspredicted to occur above 650ºC, whereas this did notoccur for CO/O2 (only heterogeneously consumed).For both reaction systems, there were intermediatetemperature windows where the observed conver-sions exceeded the diffusion limit.

CATALYSIS – INDUSTRIAL PROCESSCatalytic Conversion of Waste Plastics: Focus onWaste PVCM. A. KEANE, J. Chem. Technol. Biotechnol., 2007, 82, (9),787–795

The efficacy of Pd/Al2O3 to promote the catalyticdechlorination of PVC was demonstrated. A signifi-cant decrease (by a factor of up to 560) in the liquidfraction Cl content is seen; in addition to differences(relative to thermal degradation) in the gas phaseproduct, i.e. higher C1–C4 content with preferentialalkane formation.

CATALYSIS – REACTIONSPalladium Supported on Poly(N-vinylimidazole) orPoly(N-vinylimidazole-co-N-vinylcaprolactam) asa New Recyclable Catalyst for the Mizoroki-HeckReactionI. P. BELETSKAYA, A. R. KHOKHLOV, E. A. TARASENKO and V.S. TYURIN, J. Organomet. Chem., 2007, 692, (20), 4402–4406

The high efficiency and stability of the title catalyticsystem (1) was demonstrated in the Mizoroki-Heckreaction with active (aryl iodides and n-butyl acrylate)and less active (aryl bromides and styrene) substrates.The reaction proceeded faster using the copolymerrather than the homopolymer. (1) could be recycled.

Supercritical Carbon Dioxide and Poly(ethyleneglycol): An Environmentally Benign BiphasicSolvent System for Aerobic Oxidation of StyreneJ.-Q. WANG, F. CAI, E. WANG and L.-N. HE, Green Chem., 2007,9, (8), 882–887

Aerobic oxidation of styrene catalysed byPdCl2/CuCl can be carried out in a scCO2 and PEGbiphasic system. A high yield of acetophenone wasobtained. The PdCl2-mediated oxidation of styrenepreferentially yielded benzaldehyde using the biphasicscCO2/PEG system. Product separation and catalystrecycling are possible.

EMISSIONS CONTROLEstimating the Temperatures of the PreciousMetal Sites on a Lean NOx Trap during OxidationReactionsJ. R. THEIS and E. GULARI, Appl. Catal. B: Environ., 2007,75, (1–2), 39–51

The temperatures of the Pt sites on a 0.64 cm longmonolithic Pt/K/Al2O3 lean NOx trap were estimat-ed during CO oxidation, from the conversion of atrace amount of HC and a calibration curve of HCconversion vs. temperature. The exhaust stream con-tained 5% O2, 10% H2O, 10% CO2 and 200 ppm ofthe HC in N2. At a base temperature of 300ºC with 2%CO, the steady-state Pt temperature was ~ 130ºC higherthan the temperature of the exiting exhaust gas.


ABSTRACTSDOI: 10.1595/147106708X267335


FUEL CELLSFabrication and Performance of Pt/C Electrodesfor Low Temperature H2/O2 Fuel CellsT. UMA and M. NOGAMI, J. Membrane Sci., 2007, 302, (1–2),102–108

Pt/C electrodes (1) were fabricated and their per-formances compared at low temperature in H2/O2

fuel cells with P2O5-SiO2-PWA (phosphotungsticacid) glass membranes. The performance of (1) wasinvestigated at room temperature under humid condi-tions. A maximum power density of 30 mW cm–2 anda maximum current density of 121 mA cm–2 wereobtained for (1), with Pt/C loading of 0.15 mg cm–2

and active area of 0.49 cm2, at 30ºC and 30% RH.

Composition Effects of FePt Alloy Nanoparticleson the Electro-Oxidation of Formic AcidW. CHEN, J. KIM, S. SUN and S. CHEN, Langmuir, 2007, 23, (22),11303–11310

The catalytic activities of FexPt100–x nanoparticles (1)in the electrooxidation of HCOOH were evaluated.In chronoamperometric measurements, (1) at x ≈ 50showed the highest steady-state current density andhad long-term stability. On the basis of the CV stud-ies, the catalytic activity was: Fe42Pt58 > Fe54Pt46 ≈Fe58Pt42 > Fe15Pt85 > Fe10Pt90 > Fe63Pt37. (1) at x ≈ 50appeared to exhibit the maximum electrocatalyticactivity and stability.

Integrated One-Step PEMFC-Grade HydrogenProduction from Liquid Hydrocarbons Using PdMembrane ReactorY. CHEN, Y. WANG, H. XU and G. XIONG, Ind. Eng. Chem. Res.,2007, 46, (17), 5510–5515

A process of H2 production was developed by car-rying out the reactions during the steam reforming ofhydrocarbon fuels and H2 enrichment in a Pd mem-brane reactor. A highly H2-permeable, permselectivePd/modified α-Al2O3 composite membrane, and anactive catalyst (NiO/La2O3/alumina) for steamreforming of both higher hydrocarbons and CH4 attemperatures lower than 823 K, made one-step H2

production from steam reforming of liquid hydrocar-bons in a membrane reactor feasible.

Carbon-Supported Palladium-Cobalt-Noble Metal(Au, Ag, Pt) Nanocatalysts as Methanol TolerantOxygen-Reduction Cathode Materials in DMFCsJ. MATHIYARASU and K. L. N. PHANI, J. Electrochem. Soc., 2007,154, (11), B1100–B1105

C-supported nanoparticles of Pd-Co-M (M = Pt,Au, Ag) catalysts in a ratio of 70:20:10 were preparedthrough a reverse microemulsion method. XRDshowed well defined reflections corresponding to af.c.c. phase of Pd. The particle size after heat-treat-ment (500ºC) was ~ 20 nm. Polarisation dataindicated Pd-Co-Pt to have better ORR activity thanboth Pd-Co-Au and Pd-Co-Ag. Pd-Co-Pt also exhib-ited high MeOH tolerance.

METALLURGY AND MATERIALSGrowing Pt Nanowires as a Densely Packed Arrayon Metal GauzeE. P. LEE, Z. PENG, D. M. CATE, H. YANG, C. T. CAMPBELL andY. XIA, J. Am. Chem. Soc., 2007, 129, (35), 10634–10635

Single-crystal nanowires of Pt <111> have beensynthesised on the surface of Pt or W gauze. Byreducing the Pt precursor concentration, a layer ofnanoparticle agglomerates was eliminated, resulting ina rich surface coverage of Pt nanowires, which nucle-ate at the defective sites of the substrate.Electrochemical measurements indicated that theactive surface area of the Pt nanowire-coated gauze is2–3 times greater than that of pristine gauze.

IR Spectroscopic Observation of MolecularTransport through Pt@CoO Yolk–ShellNanostructuresS. KIM, Y. YIN, A. P. ALIVISATOS, G. A. SOMORJAI and J. T. YATES,Jr., J. Am. Chem. Soc., 2007, 129, (30), 9510–9513

FTIR spectroscopy was used to investigate the trans-port of CO to the Pt cores of Pt@CoO nanoparticlesforming CO/Pt species. Pt sites are not present on theouter surfaces of the ~ 10 nm diameter nanostruc-tures, and CO is transported to Pt adsorption sites byan activated surface diffusion process through theCoO shells surrounding ~ 2 nm diameter Pt cores.The onset of the CO diffusion through the CoO shellsoccurs at ~ 160 K. The CO/CoO species responsiblefor transport was directly observed at ~ 2147 cm–1.

The Wetting Behavior of NiAl and NiPtAl onPolycrystalline AluminaA. GAUFFIER, E. SAIZ, A. P. TOMSIA and P. Y. HOU, J. Mater. Sci.,2007, 42, (23), 9524–9528

Sessile drop experiments were performed to inves-tigate the wetting of polycrystalline alumina by NiAlalloys with or without Pt addition ranging from2.4–10 at.%. Subsequent interfacial morphology wasexamined using AFM. Pt addition was found toenhance the wettability of NiAl alloys on alumina,reducing the oxide/alloy interface energy and increas-ing the interfacial mass transport rates.

APPARATUS AND TECHNIQUEPreparation and Characteristics of Pt/ACC Catalystfor Thermoelectric Thin Film Hydrogen SensorJ. ZHANG, W. LUAN, H. HUANG, Y. QI and S.-T. TU, Sens. ActuatorsB: Chem., 2007, 128, (1), 266–272

A thermoelectric (TE) thin film H2 sensor (1) wascomposed of a Pt catalyst layer and a TE layer.Activated C fibre cloth was used as the support forthe Pt catalyst in (1). The preparation was carried outby an isometric impregnation method. (1) exhibitedgood sensing properties to H2 at room temperaturewith a high temperature difference output (47ºC), andquick response and recovery abilities (< 60 s). Goodselectivity for H2 gas was obtained at working tem-peratures below 160ºC.


Novel Nitrite Sensing Using a Palladium-polyphenosafranine Nano-compositeX. ZHU and X. LIN, Anal. Sci., 2007, 23, (8), 981–985

The title nanocomposite was synthesised by electro-chemical codeposition at a glassy carbon electrode(GCE) for fabrication of a PPS-Pd/GCE nitrite sen-sor (1). The PPS-Pd nanocomposite consisted of Pdnanoparticles which stick together due to the poly-mer, giving a Pd-embedded PPS layer structure. (1)had excellent catalytic activity toward the oxidation ofnitrite: high current sensitivity of 0.365 A/M cm–2,good reproducibility, good stability and fast response.

The Influence of Hydrogen Sulfide-to-HydrogenPartial Pressure Ratio on the Sulfidization of Pdand 70 mol% Pd–Cu MembranesO. IYOHA, R. ENICK, R. KILLMEYER and B. MORREALE,J. Membrane Sci., 2007, 305, (1–2), 77–92

The behaviour of H2S-exposed Pd membranes wasin agreement with the thermodynamic calculationsused in this investigation. Sulfidisation was resistedwhen exposed to H2S:H2 ratios below the equilibriumvalue predicted for Pd4S formation, and sulfidisationtook place when exposed to ratios above the equilib-rium values. However, 70 mol% Pd-Cu membranesresisted sulfidisation at some conditions close to theequilibrium values at which sulfidisation was expect-ed, and underwent it at some conditions at whichresistance was expected. This is attributed to the Cusegregation at the membrane surface.

CHEMISTRYEfficient, Ultrafast, Microwave-AssistedSyntheses of Cycloplatinated ComplexesN. GODBERT, T. PUGLIESE, I. AIELLO, A. BELLUSCI, A. CRISPINIand M. GHEDINI, Eur. J. Inorg. Chem., 2007, (32), 5105–5111

Cyclometallated chloridoplatinum complexes con-taining 2-phenylpyridine, 2-(2'-thienyl)pyridine (1) or4-methoxypyridine (2), as well as the cyclometallatedbenzo[h]quinoline chlorido complex with 4-methoxy-pyridine (3), were synthesised in minutes byirradiating the reaction mixture with microwaves. Thesingle-crystal X-ray molecular structures of (1), (2)and (3) are reported.

Design and Preparation of Neutral SubstitutedFluorene- and Carbazole-BasedPlatinum(II)–Acetylide ComplexesJ. BATCHA SENECLAUZE, P. RETAILLEAU and R. ZIESSEL, NewJ. Chem., 2007, 31, (8), 1412–1416

High solubility in apolar or polar solvents of the titlecomplexes was ensured by employing alkyl sub-stituents or a PEG chain grafted on the centralfluorene moiety. Further reaction on this fluoreneposition allowed the construction of a diphenylvinylgroup, which extended delocalisation. For the phos-phorescent dinuclear complexes, the absorption ofthe 3MLCT state exhibits a bathochromic shift, whichis more pronounced for the carbazole bridging unit.

Pd(SeO3), Pd(SeO4), and Pd(Se2O5): The FirstPalladium OxoselenatesA. ARNDT and M. S. WICKLEDER, Eur. J. Inorg. Chem., 2007,(27), 4335–4339

Depending on the reaction conditions, the reactionof elemental Pd with H2SeO4 in sealed glass tubes at350ºC leads to red single crystals of Pd(SeO3) or toyellow-orange single crystals of Pd(SeO4). When SeO3

is added to the reaction mixture, yellow-orange singlecrystals of Pd(Se2O5) are obtained. The IR spectrashow the typical bands for oxoselenate anions.

PHOTOCONVERSIONLuminescent Platinum(II) Complexes ContainingIsoquinolinyl Indazolate Ligands: SyntheticReaction Pathway and Photophysical PropertiesS.-Y. CHANG, J. KAVITHA, J.-Y. HUNG, Y. CHI, Y.-M. CHENG,E. Y. LI, P.-T. CHOU, G.-H. LEE and A. J. CARTY, Inorg. Chem.,2007, 46, (17), 7064–7074

[Pt(1-iqdzH)Cl2] (1a) and [Pt(3-iqdzH)Cl2] (1b)(idqzH = 1- or 3-isoquinolinyl indazole) reacted withexcess indazole, sodium picolinate or 3-trifluoro-methyl-5-(2-pyridyl) pyrazole [(fppz)H] to afford therespective luminescent complexes [Pt(1-iqdz)(L∧X)]and [Pt(3-iqdz)(L∧X)] (L∧X = 1-iqdz (2a), 3-iqdz (2b),pic (3a, 3b) or fppz (4a, 4b)). For (2), (3) and (4), pho-toluminescence in degassed CH2Cl2 revealed highquantum efficiency and short radiative lifetimes.OLEDs were fabricated using (3a).

Solid-State Luminescence Switching ofPlatinum(II) Dithiooxamide Complexes in thePresence of Hydrogen Halide and Amine GasesF. NASTASI, F. PUNTORIERO, N. PALMERI, S. CAVALLARO,S. CAMPAGNA and S. LANZA, Chem. Commun., 2007, (45),4740–4742

In the solid state, a non-luminescent Pt(II) dithioox-amide species, [Pt(R2-dto)2] (1) (dto = dithiooxamide;R = butyl), was found to adsorb gaseous HCl, yield-ing a tight ion pair species which exhibitsphotoluminescence. The process is quantitativelyreversed on heating or by exposing the sample toNH3 vapours. The luminescence of (1) can beswitched on or off by the different gas inputs, yield-ing gas-activated luminescent molecular logic gates.

SURFACE COATINGSVapor Deposition of Ruthenium from anAmidinate PrecursorH. LI, D. B. FARMER, R. G. GORDON, Y. LIN and J. VLASSAK,J. Electrochem. Soc., 2007, 154, (12), D642–D647

Atomic layer deposition and pulsed CVD wereemployed to deposit Ru thin films (1) from thevolatile bis(N,N'-di-tert-butylacetamidinato)rutheni-um(II) dicarbonyl. (1) are fine-grained polycrystallineRu (< 0.2% impurities). Ru grew as a continuous, elec-trically conductive, pinhole-free film on WN films.The resistivities of (1) match those of sputtered Ru.

58

CATALYSIS – APPLIED AND PHYSICAL ASPECTSNanostructured Ruthenium CatalystsUNIV. DI PISA World Appl. 2007/085,463

Nanostructured metal catalysts are prepared byreduction of a precursor of formula MnXy or HxMnXy,where M is a metal selected from Ru, Rh, Pd, Pt, Ir,Re, Ni, Cu, Fe or Au, preferably Ru, and X is ananion. Reduction is carried out by heating in a low-boiling alcoholic solvent or cosolvent at 10–150 barand 50–400ºC. A stabilising agent may optionally beadded. The catalyst can be used for selective hydro-genation of organic compounds.

Nanometer Porous Platinum Alloy CatalystSHANDONG UNIV. Chinese Appl. 1,962,057

A PtAu alloy catalyst has thickness 10–200 μm,width 0.5–2 cm and length 2–10 cm. Pore diameterand wall size are controllable and adjustable between2–300 nm. The composition contains (in at.%):25–100 PtAu and 0–75 Cu. Alternatively Pt, Au or Cumay be varied from 0–100 at.%, at least two being > 0.

CATALYSIS – INDUSTRIAL PROCESSProduction of Acetic AcidBP CHEM. LTD World Appl. 2007/085,791

A continuous process is claimed for the productionof acetic acid by carbonylation of MeOH and/or areactive derivative thereof with CO in the presence ofan Ir catalyst, MeI cocatalyst, H2O, acetic acid andmethyl acetate plus promoters Ru and one of Nb orTa. The molar ratio of promoters:Ir is between > 0:1and 15:1, and of Ir:Ru:(Nb or Ta), 1:(1–10):(1–10).The concentration of each promoter is < 8000 ppm.Carbonylation is carried out at 1–20 MPaG and150–220ºC in one or more reaction zones.

Asymmetric Hydrogenation of Acrylic AcidDSM FINE CHEM. AUSTRIA GmbH European Appl. 1,830,958

A process for the asymmetric hydrogenation ofacrylic acid derivatives uses a catalyst system contain-ing Ru, Rh or Ir, with a chiral P ligand and an achiralP ligand, in the presence of one or more H donors.The solvent system may be 2-propanol with H2O in aratio of 3:1–6:1. H2 may be used as the H donor.Reaction is carried out between –20ºC and 120ºC.

CATALYSIS – REACTIONSBiphosphine Ruthenium ComplexesJOHNSON MATTHEY PLC European Appl. 1,849,972

A chiral catalyst is formed from the reactionbetween a Ru compound, a chiral bis(phosphine)such as BINAP and a chiral diamine. The catalyst maybe used for asymmetric hydrogenation of ketones andimines, including alkyl ketones of formula RCOR'where R and R' are substituted or unsubstituted, sat-urated or unsaturated C1–C20 alkyl or cycloalkylwhich may be linked and form part of a ring structure.

EMISSIONS CONTROLCatalysed Soot FilterJOHNSON MATTHEY PLC World Appl. 2007/099,363

An exhaust system for a lean burn internal combus-tion engine includes a CSF; a control unit; a means toincrease the content of hydrocarbons and/or CO inexhaust gas flowing into the CSF, increase tempera-ture and combust particulate matter; plus a catalysedsensor. The CSF catalyst includes at least one Ptgroup metal, preferably Pt or both Pt and Pd. The cat-alyst in the sensor is preferably the same as in the CSF.

Catalyst for Exhaust Gas PurificationICT CO LTD European Appl. 1,834,694

A catalyst for exhaust gas purification is claimed tohave excellent ignition and NOx purification perfor-mance. The first catalytic component consists of Pdand Ba supported on a refractory inorganic oxide, andthe second contains Rh and/or Pt supported onanother refractory oxide. The components arearranged in one surface and one lower layer. Themolar ratio of Ba/Pd is > 0 and ≤ 2. Each catalyticcomponent is present in 10–300 g l–1 catalyst.

FUEL CELLSMethod for Producing ElectrocatalystNISSAN MOTOR CO LTD U.S. Appl. 2007/0,231,620

A PtIr alloy fuel cell catalyst is produced by mixingan organic solvent containing surfactant with an aque-ous solution of an Ir compound, to form an invertedmicelle. The Ir compound is insolubilised to form fineIr particle aggregate, then impregnated with an aque-ous solution of Pt compound. The Pt compound isthen reduced to Pt metal, to give PtIr particles, whichare then supported on a conductive carrier and fired.

Iron-Platinum ElectrocatalystPUSAN NATL. UNIV. Korean Appl. 2007-0,047,959

A method for producing a carbon nanofibre-supported FePt fuel cell catalyst is claimed. Carbonnanofibres are pickled in a nitrate solution to removeimpurities, then sealed into a first bath of acetonecontaining Pt ions. The adsorbed Pt is then reducedto metallic Pt particles. The process is repeated usinga second sealed bath of acetone containing Fe ions.

METALLURGY AND MATERIALSMetallic Temporary TattooT. D. WILLIAMS U.S. Appl. 2007/0,184,094

A decorative temporary tattoo may be formed frommetal leaf using metals such as Pt, Au, Ag, Cu, Al orcoloured metal leaf. A template formed from a mate-rial such as vinyl is attached to the skin, a skin-safeadhesive is applied to the area to be decorated, thenthe metal leaf is contacted with the adhesive. Thetemplate is removed to leave a metal leaf tattoo on theskin. The process may be repeated.


DOI: 10.1595/147106708X266183

NEW PATENTS

High Temperature Shape Memory AlloyR. D. NOEBE et al. U.S. Appl. 2007/0,204,938

The title alloy, with high specific work output anddimensional stability under repeated actuation, ismade from (Ni + Pt + Y)xTi(100–x), where 49 ≤ x ≤ 55,and contains 10–30 at.% Pt and 0–10 at.% Y, whereY = Pd, Au and/or Cu. The alloy has a matrix phasewhere [Ni + Pt + Y] > 50 at.%. One or more of O,C, B or N may optionally be incorporated. The tran-sition temperature is > 100ºC and the alloy hasincreased processability at > 800ºC. The alloy may beused in a high temperature actuator.

Iridium Heat-Resistant ContainerTANAKA KIKINZOKU KOGYO KK

Japanese Appl. 2007-119,296A thin-walled heat-resistant container is made from

Ir of thickness ≤ 0.3 mm, and is formed by electro-lysis of a molten salt containing an Ir salt. Impuritiesother than noble metals are ≤ 100 ppm and noblemetals other than Ir are ≤ 10,000 ppm. The containermay be used for a Bridgman crucible or as a heat-resistant cell for thermal analysis apparatus.

APPARATUS AND TECHNIQUERhodium Spark PlugDENSO CORP U.S. Appl. 2007/0,194,681

A spark plug for an internal combustion engineincludes a ground electrode chip and a centre elec-trode chip made from Rh with 0.3–2.5 wt.% of anadditive, selected from rare earth, Group IVA orGroup VA elements such as Sc, Y, La, Zr, Hf, Nb orTa. Alternatively, either the ground or centre elec-trode chip may be made from Pt or Ir, preferably Pt.Enhanced resistance to wear from exposure to sparksand oxidation is claimed.

X-Ray SourceSHIMADZU CORP Japanese Appl. 2007-123,022

An X-ray source with small X-ray focus and a pre-cise and stable electron beam diameter is claimed,together with a target made from Rh particles fixed inplace along with a Be thin film. An electron beam iscollided with the target, to generate X-rays from Rhand Be. Since X-rays generated from Be are of lowenergy, the diameter of the Rh particles becomes thediameter of the X-rays’ focus.

BIOMEDICAL AND DENTALImplantable Stimulation ElectrodeMEDTRONIC INC European Appl. 1,848,495

An implantable medical electrode is fabricated byroughening the surface of an electrode made from Pt,PtIr, Ti or Nb; cleaning; then depositing a coating ofvalve metal oxide including Ru oxide, by a sputteringprocess optimised to minimise electrode impedanceand post-pulse polarisation. There may optionally bean adhesion layer of Ti or Zr between the electrodeand the Ru oxide coating.

Osmium Compounds for Treatment of PsoriasisA. HELLER U.S. Appl. 2007/0,184,095

Pharmaceutically acceptable topical compositionsfor the treatment of psoriasis using compounds of aPt group metal, preferably Os, are claimed. The nom-inal valency of Os is 4–8, and at least 3 atoms adjacentto Os are O or are H2O-exchangeable under physio-logical conditions. Compounds may include OsO4.The composition may be water- or oil-based and maybe applied from a dressing attached to the skin toeffect controlled release of the Os compound.

ELECTRICAL AND ELECTRONICSSilica-Capped FePt NanomagnetsRENSSELAER POLYTECH. INST. World Appl. 2007/123,846

Nanoparticles for a magnetic storage device includea magnetic metal core containing Pt and at least oneother metal selected from Fe or Co, preferably Fe,and an outer shell of SiO2, TiO2, metal nitride ormetal sulfide, preferably SiO2. Average size of themetal core is ~ 4–21 nm and average thickness of theouter shell is ~ 1–100 nm. Coercivity of the nanopar-ticle is ≥ 800 mT and it retains its size and shape afterannealing at ~ 600ºC for 30 mins.

Perpendicular Magnetic Recording MediumFUJITSU LTD U.S. Appl. 2007/0,231,608

A perpendicular magnetic recording medium for amagnetic storage unit includes a substrate; a softmagnetic underlayer; a seed layer of amorphous non-magnetic material selected from Ta, Ti, Mo, W, Re, Hfand Mg; an oxidation prevention layer of Pt, Au or Ag,of thickness ≥ 2.0 nm; an underlayer of Ru or Ru alloyh.c.p. crystal grains with an air gap; then a magneticrecording layer of Co, CoPt, CoCr, CoCrPt, CoCrTaor CoCrPt-M, where M = B, Ta, Cu, W, Mo or Nb.

SURFACE COATINGSPalladium Plating SolutionELECTROPLAT. ENG. JPN. LTD U.S. Appl. 2007/0,205,109

A solution for plating a Pd film includes a solublePd salt, selected from an amino group-based or anammonia-based Pd complex, plus a Ge compoundand an electrically conductive salt. The concentrationsare: 0.1–50 g l–1 Pd salt, 10–400 g l–1 electrically con-ductive salt and 0.1–1000 mg l–1 Ge. Plating is carriedout at 25–70ºC, pH 6.0–10.0 and 0.1–5.0 A dm–2.

Platinum Thin Film FormationNIPPON TELEGR. TELEPH. CORP

Japanese Appl. 2007-131,924A process for forming a Pt thin film on SiO2 is

claimed. A Si substrate is formed from single crystalSi in which the (100) plane is the main surface. Alayer of SiO2 is formed or deposited on the surface,for example by thermal oxidation or by CVD. Anelectron cyclotron resonance sputtering processusing a Pt target is used to deposit a Pt thin film witha thickness of ~ 200 nm.



FINAL ANALYSIS

Particle Size Analysis of SupportedPlatinum Catalysts by TEM

Particle size analysis on catalysts has beencarried out for many years as the most direct wayto predict the effective surface area available forcatalytic activity. There are many techniquesavailable for characterising the particle size in therange between 100 μm and 10 nm. However, onlyX-ray diffraction (XRD) and transmission electronmicroscopy (TEM) can conveniently provideinformation below 10 nm.

These two techniques differ significantly intheir approach. XRD analysis provides informa-tion on crystallite size rather than particle size(particles could be formed of several crystallitegrains). Furthermore, XRD provides an averageparticle size from a volume average across thewhole sample, rather than specific particles. TEM,on the other hand, provides particle size analysisfrom individual particles observed in a trans-mission electron micrograph. The technique gives

localised size information from the areas of sam-ple where the images are obtained. The counting iscarried out one by one manually, or on a large scaleby digital particle size analysis. The results arenumber-averaged rather than volume-averaged.The analysis is based on ‘thresholding’ the intensi-ties from each pixel of an image, and exploiting thedifferences in intensity between particles andthe background.

Digital processing of particle images within asmooth background is fairly straightforward, pro-vided there is a marked intensity differencebetween the particle and the background.However, for supported particles where the back-ground intensity varies due to the uneventhickness and surface features of the support, it isvery complicated. The human eye does a better jobin this situation, because it looks at a particle with-in its immediate surrounding rather than

DOI: 10.1595/147106708X264095

(a)

20 nm

(b)

20 nm

201816141210

86420

Num

ber o

f Pt p

artic

les

1 2 3 4 5 6 7 8 9 10 >10Particle size, nm

(d)

(c)

20 nm

Fig. 1 The digital image processing of a bright fieldtransmission electron micrograph of platinum particles(dark) on a carbon catalyst support (bright): (a) originalimage; (b) threshold of image without background cor-rection; (c) threshold with background correction; and(d) the particle size distribution obtained

considering it as part of the whole intensity scaleof the image. Digital analysis relies on absoluteintensities, and if the intensity of a thick part of asupport were the same as the intensity within aparticle, both would be recognised as particleand/or support. The only way to resolve this con-flict is to pre-process the digital image, to convertthe localised intensity differences between parti-cles and the support to absolute intensitydifferences which are global to the image (seeFigure 1(b)).

There are a number of approaches for digitallyreducing the background levels and boosting theglobal intensity differences between particle andsupport. The method used here is based on divid-ing the image into equivalent areas andthresholding these areas locally, in very much thesame way as the human eye. Figure 1 shows thesteps used in image analysis, with a view to obtain-ing particle size distributions using TEM. InFigure 1(a), the difference in intensity between theparticles and support is due mostly to the differ-ence in atomic number between platinum andcarbon. Figure 1(c) shows that thresholding withbackground correction improves the detection ofindividual particles.

The next stage is to deselect some of these par-ticles, especially ones that do not truly represent afull particle due to overlapping or being at the edge

of the image. This is followed by calculating thestatistical variables, such as the area, major andminor axes, and aspect ratio of the particle. Thesevariables can then be plotted to give a chart show-ing the distribution of size vs. number of platinumparticles, such as that shown in Figure 1(d).

The process relies on the assumption of ahomogeneous distribution of particle sizes, whichcan be checked by moving to different parts of thesample. It is also important to remember that theparticle sizes are calculated from projected vol-umes; although this assumption holds very well formost catalyst nanoparticles, if the particles are farfrom spherical (for example, rods or disks), thenthis assumption would not hold. In this case, amore laborious tomography routine would need tobe developed.

D. OZKAYA

The Author

Dogan Ozkaya works as a Principal Analyst,responsible for electron microscopy in theAnalytical Department at the JohnsonMatthey Technology Centre, SonningCommon, U.K. He holds a Ph.D. inMaterials Science and Metallurgy from theUniversity of Cambridge. He carried outpostdoctoral research related to electronmicroscopy in several universitydepartments, including the CavendishLaboratory, University of Cambridge, andthe Materials Department, University ofOxford, before joining Johnson Matthey in2003. He has been involved in research onplatinum group metal catalysts for 12 years.

62Platinum Metals Rev., 2008, 52, (1)

Platinum Metals ReviewJohnson Matthey Plc, Precious Metals Marketing, Orchard Road, Royston, Hertfordshire SG8 5HE, U.K.

E-mail: [email protected]://www.platinummetalsreview.com/

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