1 Institute of Isotopes, Budapest, Hungary; 2 Research Institute for Technical Physics and Materials...

1Institute of Isotopes, Budapest, Hungary;2Research Institute for Technical Physics and Materials

Science, Budapest Hungary;3Chemical Physics of Materials, ULB, Brussels, Belgium

Gold and silver catalysts for abatement of Gold and silver catalysts for abatement of environmentally harmful materials: environmentally harmful materials:

modelling the structure dependencymodelling the structure dependency

Gold and silver catalysts for abatement of Gold and silver catalysts for abatement of environmentally harmful materials: environmentally harmful materials:

modelling the structure dependencymodelling the structure dependency

Krisztina FreyKrisztina Frey11, Gábor Pető, Gábor Pető22, , Viacheslav IablokovViacheslav Iablokov33, Norbert , Norbert

KruseKruse33 and László Guczi and László Guczi11

Krisztina FreyKrisztina Frey11, Gábor Pető, Gábor Pető22, , Viacheslav IablokovViacheslav Iablokov33, Norbert , Norbert

KruseKruse33 and László Guczi and László Guczi11

INTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTION

Automotive exhaust contains high concentrations of NOx, CO and

hydrocarbons, which are harmful to human health.

All commercial solutions (Three Way Catalysis, Selective Catalytic

Reduction, Storage, etc.) are based on platinum, palladium and

rhodium metal.

The present work is aimed at exploring the The present work is aimed at exploring the

potential of a new generation of potential of a new generation of

catalysts, based on catalysts, based on gold gold and and silversilver, to , to

replace the more expensive platinum and replace the more expensive platinum and

rhodium metals.rhodium metals.

GOAL of the present workGOAL of the present workGOAL of the present workGOAL of the present work

Provide sound understanding of the intrinsic properties of silver Provide sound understanding of the intrinsic properties of silver

and gold based model catalysts:and gold based model catalysts:

1.1. Compare activities CO oxidation between silver and gold Compare activities CO oxidation between silver and gold

supported catalysts.supported catalysts.

2.2. Study gold particles and gold films either in presence or Study gold particles and gold films either in presence or

absence of metal-oxide supports (TiOabsence of metal-oxide supports (TiO22 and FeO and FeOxx). What is the ). What is the

effect of metal-oxides?effect of metal-oxides?

3.3. Demonstrate the CO oxidation activity in sandwiched layers of Demonstrate the CO oxidation activity in sandwiched layers of

gold/metal-oxide systems („inversed” system). gold/metal-oxide systems („inversed” system).

4.4. Use high resolution microscopy (AFM) and spectroscopy (SIMS, Use high resolution microscopy (AFM) and spectroscopy (SIMS,

XPS) to characterize the morphology of the used layered XPS) to characterize the morphology of the used layered

catalysts. catalysts.

Justification of the ApproachJustification of the ApproachJustification of the ApproachJustification of the Approach

Unique electronic and Unique electronic and morphologicalmorphological properties properties may developmay develop when dimensions when dimensions reach the nanoscale.reach the nanoscale.

These changes These changes may alter the chemay alter the chemical reactivitymical reactivity..

Develop an understanding Develop an understanding of of the key features the key features ofof nanoscale nanoscale materials is a first step towards the materials is a first step towards the control and design of highly selective catalysts at control and design of highly selective catalysts at otherwiseotherwise optimum catalytic activity. optimum catalytic activity.

Ag/TiOAg/TiO22

Sample preparationSample preparation

Ag/TiOAg/TiO22


Ag(COO)Ag(COO)22 →→ Ag + 2 CO Ag + 2 CO22

Ag/TiO2 catalysts have been prepared via oxalate co-precipitationoxalate co-precipitation of AgNO3 and Ti(OCH(CH3)2)4 as precursors than TPO (temperature-programmed oxidation). Ag loadings in the catalysts were 2, 4, 7 and 10% (w/w).

0 2000 4000 6000 8000 10000Time (s)

Par

tial p

ress

ure

(a.u

.)

O2

CO2

CO

300

400

500

600

700

800

Tem

perature (K)

Temperature

10% Ag/TiO2

0 2000 4000 6000 8000 10000Time (s)

Par

tial p

ress

ure

(a.u

.)

O2

CO2

CO

300

400

500

600

700

800

Tem

perature (K)

Temperature

2% Ag/TiO2

TPOTPO

Ag/TiOAg/TiO22

Sample characterizationSample characterization

Ag/TiOAg/TiO22

Sample characterizationSample characterization

(HR)TEM(HR)TEM4%Ag/TiO4%Ag/TiO22 10%Ag/TiO10%Ag/TiO22

Ag

0 1000 2000 30000

500

1000

1500

CO

2 fo

rmed

, m

ol/g

cat

reaction time, s

2%Ag/TiO2

7%Ag/TiO2

10%Ag/TiO2

In circulate system: In circulate system: 9 mbar CO and9 mbar CO and 9 mbar 9 mbar O O22 and 162 mbar He and 162 mbar He at 313 Kat 313 K

Ag/TiOAg/TiO22

CO oxidation in circulate system CO oxidation in circulate system

Ag/TiOAg/TiO22

CO oxidation in circulate system CO oxidation in circulate system

EEaa=13-25 kJ/mol=13-25 kJ/mol

Ag/TiOAg/TiO22

CO oxidation in flow systemCO oxidation in flow system

Ag/TiOAg/TiO22

CO oxidation in flow systemCO oxidation in flow system

CO+OCO+O22 mixture of 2% each, using Ar as diluent with a flow mixture of 2% each, using Ar as diluent with a flow

rate of 50 ml/minrate of 50 ml/min..

300 350 400 450 500 5500

20

40

60

80

100

10% Ag 2% Ag 7% Ag

CO

con

vers

ion

(%

)

Temperature (K)

Au/SiOAu/SiO22/Si(100) catalysts/Si(100) catalystsAu/SiOAu/SiO22/Si(100) catalysts/Si(100) catalysts

CharacterizationCharacterizationCharacterizationCharacterization

TEMTEM particle size.

AFM AFM particle size and surface roughness.

SEM SEM scanning electron microscopy.

SIMS,SIMS, XPSXPS surface composition.

XPS, UPSXPS, UPS electron structure.

CO oxidationCO oxidation catalytic activity.

Effect examination:

Characterization:

The samples were treated in 200 The samples were treated in 200 mbarmbar H H22 at 573 K for at 573 K for

1 h, then at 803 K CO oxidation was performed in an all 1 h, then at 803 K CO oxidation was performed in an all

glass made circulation reactor connected to a QMS. A glass made circulation reactor connected to a QMS. A

mixture of mixture of 9 9 mbar CO + mbar CO + 1818 mbar O mbar O22 + 15 + 1533 mbar He was mbar He was

used. The initial rate of COused. The initial rate of CO22 formation was related to the formation was related to the

geometrical surface of the wafer (cc. 0.5 cmgeometrical surface of the wafer (cc. 0.5 cm22). ).

CO oxidationCO oxidationCO oxidationCO oxidation

Au/SiOAu/SiO22/Si(100)/Si(100)


Au/SiOAu/SiO22/Si(100)/Si(100)


Si SiO2 Au

Implantation(40 keV, 1015 atom/cm2)

Evaporation

hAu= 10 nm

hAu= 80 nm

Modelling „inverse” Modelling „inverse” FeOFeOxx/Au and TiO/Au and TiO22/Au system/Au system

Modelling „inverse” Modelling „inverse” FeOFeOxx/Au and TiO/Au and TiO22/Au system/Au system

80 nm Au film/SiO2/Si(100) Au nanoparticles/SiO2/Si(100)

Si Au FeOx, TiO2

Laser ablation (PLD)

SiO2

0 500 1000 1500 2000 2500 30000

5

10

15

20

25

30

35

CO

2 fo

rmed

, m

ol/c

m2

reaction time, s

FeOx/Au nanoparticles/SiO

2/Si(100)

FeOx/Au layer/SiO

2/Si(100)

FeOx/SiO

2/Si(100)

FeOFeOxx/Au/SiO/Au/SiO22/Si(100)/Si(100)

CO oxidationCO oxidation



In circulate system: In circulate system: 9 mbar CO9 mbar CO, 18 mbar, 18 mbar O O22 and 162 mbar He and 162 mbar He at 803 K at 803 K

CO oxidationCO oxidationCO oxidationCO oxidation

Au nanoparticles

0,00E+00

5,00E-03

1,00E-02

1,50E-02

2,00E-02

2,50E-02

1 2 3 4samples

r o/

mo

l cm

-2s

-1

SiO2/Si(100)

Au/SiO2/Si(100)

FeOx/Au/SiO2/Si(100)

FeOx/SiO2/Si(100)

80 nm Au film

0,00E+00

5,00E-03

1,00E-02

1,50E-02

2,00E-02

2,50E-02

1 2 3 4samples

r o/

mol

.cm

-2.s

-1

SiO2/Si(100)

Au/SiO2/Si(100)

FeOx/Au/SiO2/Si(100)

FeOx/SiO2/Si(100)





CO oxidationCO oxidationCO oxidationCO oxidationTiOTiO22/Au/SiO/Au/SiO22/Si(100)/Si(100)


TiOTiO22/Au/SiO/Au/SiO22/Si(100)/Si(100)


0 1000 2000 3000 40000

20

40

60

80

CO

2 fo

rmed

, m

ol/

cm2

reaction time, s

TiO2/SiO

2/Si(100)

TiO2/8 nm Au layer/SiO

2/Si(100)

8 nm Au layer/SiO2/Si(100)

Au nanoparticles on SiOAu nanoparticles on SiO22/Si(100)/Si(100)Au nanoparticles on SiOAu nanoparticles on SiO22/Si(100)/Si(100)

AFMAFM

80 nm Au film/SiO80 nm Au film/SiO22/Si(100): AFM/Si(100): AFM80 nm Au film/SiO80 nm Au film/SiO22/Si(100): AFM/Si(100): AFM

80 82 84 86 88 90

Inte

ns

ity

a.u

.

Binding energy, eV

80 nm film Au/SiO2/Si(100)

10 nm implanted Au/SiO2/Si(100)

x10

Au characterizationAu characterizationBulk or nanoBulk or nano??

Au characterizationAu characterizationBulk or nanoBulk or nano??

Au 4f XPS Au 4f XPS

bulk

nanonano

Si 2p XPS Si 2p XPS Si 2p XPS Si 2p XPS

Au nanoparticles

80 nm Au film covered

uncovereduncovered

96 98 100 102 104 106 108 110

Inte

nsi

ty, a

.u.

Binding energy, eV

FeOFeOxx/Au/SiO/Au/SiO22/Si(100)/Si(100)FeOFeOxx/Au/SiO/Au/SiO22/Si(100)/Si(100)

196,5 197,0 197,5

MS

sig

na

l, a

.u.

mass (m/z)

Au/SiO2/Si(100)

Fe/Au/SiO2/Si(100)

80 nm Au film/SiO2/Si(100)

Au nanoparticles/SiO2/Si(100)SIMSSIMS

SEMSEM

OOn the surface of Fen the surface of Fe22OO33 covered covered Au/SiOAu/SiO22/Si(100) /Si(100) (Au nanoparticles (Au nanoparticles

& 80 nm thick Au& 80 nm thick Au film film)) no goldno gold was detected was detected..

705710715720725730735

Binding energy, eV

Inte

nsi

ty,

a.u

.

1

2

aFe 2p

Fe3+

Fe2+satellite

526528530532534536

Binding energy, eV

1

2

bO 1s

O2-

O=C

OH

XPS spectra of XPS spectra of FeOFeOxx/Au layer/SiO/Au layer/SiO22/Si(100)/Si(100)

XPS spectra of XPS spectra of FeOFeOxx/Au layer/SiO/Au layer/SiO22/Si(100)/Si(100)

FeFe22OO33 (Fe (Fe3+3+) and FeO (Fe) and FeO (Fe2+2+))

Effect of temperature used in CO Effect of temperature used in CO oxidation on the surface: cracks ?oxidation on the surface: cracks ?Effect of temperature used in CO Effect of temperature used in CO

oxidation on the surface: cracks ?oxidation on the surface: cracks ?

nano Au

FeOx/nano Au

80 nm Au

FeOx/80 nm Au

SEM SEM after 5 min reactionafter 5 min reaction

0.1 m

0.1 m

0.1 m

0.1 m

Core level binding energy is shifted to higher value when gold film was Core level binding energy is shifted to higher value when gold film was transferred into gold nanoparticles.transferred into gold nanoparticles.

When When anan “inverse” “inverse” Au/FeOAu/FeOxx iis fabricated bys fabricated by FeO FeOxx deposition onto deposition onto either either

Au nanoparticles/SiOAu nanoparticles/SiO22/Si(100) or 80 nm /Si(100) or 80 nm Au film/Au film/SiOSiO22/Si(100) reference /Si(100) reference

samplesample,, the the catalytic activity in the CO oxidation is enhanced compared catalytic activity in the CO oxidation is enhanced compared to to both both Au/SiOAu/SiO22/Si(100) and FeO/Si(100) and FeOxx/SiO/SiO22/Si(100). /Si(100).

The activity enhancement is larger for nano-type Au/FeOThe activity enhancement is larger for nano-type Au/FeOxx than for bulk- than for bulk-

type Au/FeOtype Au/FeOxx co-operation. The gold effect co-operation. The gold effect isis indirect, indirect, becausebecause Au Au is is not not

exposed to the surface exposed to the surface and it and it modifies the catalytically working FeOmodifies the catalytically working FeOxx..

The activity of theThe activity of the TiOTiO22/SiO/SiO22/Si(100) was higher than that of /Si(100) was higher than that of

TiOTiO22/Au/SiO/Au/SiO22/Si(100), which indicated an inhibiting effect of gold layer/Si(100), which indicated an inhibiting effect of gold layer

underneath the TiOunderneath the TiO22 overlayer. overlayer.

Ag/TiOAg/TiO22 catalysts with different Ag loadings (2, 4, 7 and 10% (w/w)) the catalysts with different Ag loadings (2, 4, 7 and 10% (w/w)) the

best conversion performance was obtained in a CO/Obest conversion performance was obtained in a CO/O22=1:1 mixture over =1:1 mixture over

10% Ag/TiO10% Ag/TiO22 for which the temperature of 50% CO conversion was for which the temperature of 50% CO conversion was

TT5050=333 K =333 K

We can conclude thatWe can conclude that

Thank you for your attention!Thank you for your attention!

Au Au nanoparticles nanoparticles on SiOon SiO22/Si(100):/Si(100):

before and after CO oxidationbefore and after CO oxidation

Au Au nanoparticles nanoparticles on SiOon SiO22/Si(100):/Si(100):

before and after CO oxidationbefore and after CO oxidation

beforebefore afterafter

J. Am. Chem. Soc., 125(14), 4332-4337 (2003)

1 6 1 2 8 4 0

8 0 0 0

1 0 0 0 0

1 2 0 0 0

1 4 0 0 0

1 6 0 0 0

1 8 0 0 0

Inte

nsi

ty (C

ount

s)

Binding Energy (eV)

After CO oxidationAfter CO oxidationAfter CO oxidationAfter CO oxidation

BULK!!!BULK!!!

10 nm implanted Au/SiO2/Si(100) XPS spectrum

1h catalytic reaction!

J. Am. Chem. Soc., 125(14), 4332-4337 (2003)

The aggregated Au particles shows „bulk type” electron structures.


Is FeOIs FeOxx porous? porous?


Is FeOIs FeOxx porous? porous?

0 500 1000 1500 20000

5

10

15

20

25

30

CO

2, m

ol/

cm

2

reaction time,s

10 nm FeO10 nm FeOxx/Au/SiO/Au/SiO22/Si(100)/Si(100)

40 nm FeO40 nm FeOxx/Au/SiO/Au/SiO22/Si(100)/Si(100)

40 nm FeOx/SiO2/Si(100)

In case of thick FeOIn case of thick FeOxx layer no effect of underlying gold on the catalytic activity layer no effect of underlying gold on the catalytic activity

of FeOof FeOxx..

AFM picture afterAFM picture after 5 min. reaction5 min. reaction

AFM picture afterAFM picture after 5 min. reaction5 min. reaction

1 Institute of Isotopes, Budapest, Hungary; 2 Research Institute for Technical Physics and Materials...

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Transcript of 1 Institute of Isotopes, Budapest, Hungary; 2 Research Institute for Technical Physics and Materials...