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Ind. Eng. C h e m . Res 1987,26, 1495-1500 1495Activity and Selectivity of Ni-Mo/HY Ultrasta bleZeolites for Hydroisomerization and H ydrocrack ing ofAlkanes?

M. Isabel VBzquez and Ag us th EscardinoDepar tamento de Zngenieria Q uh ic a , Uniuersi ta t de ValPncia , 46100 Burjassot Valenc ia) ,S p a i nAvelino Corma*Inst i tu to de Catdl is is y Pe troleoquimica , CSIC , 28006 Madrid , Spa inThe hydroisomerization and hydrocracking of n-heptane have been studied on a series of Ni-Mo/HYultrastable zeolite catalysts a t 300-350 O reaction temperature and 25 kgcm-2 of t otal pressure.Th e product distribution in the isomerized fraction and in the cracked fraction has been discussedfrom the poin t of view of a typical bifunctional mechanism. It has been found that th e Ni/(Ni +Mo) atomic ratio of the catalyst has a strong influence on th e activity, and a maximum is foundfor a Ni/(Ni + Mo) N 0.5. The selectivity to hydroisomerization, hydrocracking, and hydrogenolysisalso depends on the Ni/(Ni + Mo) ratio and any of them could be maximized by an adequatecombination of the hydrogenating and the acid function.

Hydrocracking is one of the three basic processes inpetroleum refining used t o convert heavy oils into morevaluable products. It does the work by converting largehigh boiling point molecules into lower boiling productsby simultaneoushydrotreating and cracking carbon-carbnbonds. Since the process needs to carry out two functions,typical catalysts should be bifunctional and incorporateboth hydrogenation and cracking components. Hydro-cracking is a very flexible process which allows one toobtain a broad range of saturated products ranging fromhigh yields of liquid petroleum gas to middle distillate witha high octane number. This flexibility is due not only tothe process itself but mostly to the catalyst design (Ward,1983). Indeed the cracking and hydrogenation capacitystrongly affect the product distribution that results.Concerning the cracking function, it is well-known tha tcracking is an acid-catalyzed reaction; hence, it is desirableto have one acid function in which the strength and num-ber of acid sites could be controlled. This is achieved,actually, by using some zeolites such asY, ZSM-5,erionite,and mordenite (Bolton, 1976; Chen et al., 1977; Steijns etal., 1981; Haynes et al., 1983; Franck and Le Page, 1981;Ward, 1975; Weitkamp et al., 1983; Guisnet and Perot,1984). Among them, Y zeolites are the most widely used,while the others are used in the cases which require re-actions controlled by pore geometry.The hydrogenating function is given by either noblemetals such as Pt and P d (Gallei et al;, 1981; Riberiro etal., 1982; Weitkamp and Ernst, 1985) or combinations ofnon-noble metals of groups 9 and 10 (Co, Ni) and the

metals of group 6 (Mo, W) (Ward, 1983; Ternan andParson, 1979; Mooi, 1980). In the latest case the hydro-genation activity depends, besides on the particular com-bination of non-noble metals, on the atomic ratio of those.In the present work, we study the influence of the acid and~~ * To whom correspondence should be addressed.t In this paper the periodic group notation is in accord withrecent actions by IUPAC and ACS nomenclature committees. Aand B notation is eliminated because of wide confusion. GroupsIA and IIA become groups 1 and 2. The d-transition elementscomprise groups 3 through 12, nd t he p-block elements comprisegroups 13 through 18. (Note that the former Roman numberdesignation is preserved in the last digit of the numbering: e.g.,I11- and 13.)

the hydrogenation component, in a Ni-Mo/HY ultrastablezeolite, on the activity and selectivity for hydro-isomerization and hydrocracking of n-heptane.Experimental Section

Materials. The zeolite used in this study was a HYultrastable zeolite (HYUS), with a unit cell dimension, a= 24.40 A It was prepared from a NaY Linde SK-40(Si/Al = 2.4) zeolite by repeated ion exchange with am-monium acetate. Each exchange was followed by deep bedcalcination at 550 C for 3 h, until the final Naf contentof the zeolite was lower than 2 % of the initial value. TheBET area of the HYUS zeolite was 450 m2.g-I, and thisvalue was not influenced by removal of Na+. The nickeland molybdenum were incorporated in the HYUS zeoliteseparately by vacuum impregnation at 70 C from anaqueous solution of nickel nitrate and ammonium hepta-molybdate, respectively. After each impregnation, thesample was dried at 110 C for 6 h and then calcined intwo steps. The first, to decompose the salt, was carriedout in air flow at 450 C for 2 h and the second at 550 Cfor 3 h. The final NiO and Moo3 content of the catalystwas determined by the following procedure: 0.5 g of themoisture-free sample was introduced into a platinumcrucible and covered by 10 g of an equimolecular Na2C-03-KzC0, mixture and 0.5 g of B03H3. This mixture washeated at 1100 C and maintained for about half an houruntil complete solution was obtained. When the melt hadpartially cooled, this was dissolved with HCl ( l: l) , and thesolution was gauged and analyzed by atomic absorptionspectroscopy.In order to study the influence of the Ni/ (Ni + Mo)atomic ratio on the activity, various catalysts with differentNiO content and a 8 w t Moo3 content were prepared.High-purity n-heptane (>99.5%) and Hz (>99.9%) wereused as reactants without further purification.Apparatus and Procedure. The experiments werecarried out, a t temperatures of 300,330, and 350 C and25 kg.cm-2 total pressure, in a continuous tubular, plugflow, stainless steel reactor. After preparation, the catalystawere pelletized, crushed, and sieved, and the particle sizefraction of 0.125-0.250 mm was selected. In each exper-iment the weight of catalyst was varied for obtainingdifferent conversions and the W / F o atio (weight of ca t -

0888-5885/87/2626-1495 01.50/0 1987 American Chemical Society

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1496 Ind. Eng. Chem. Res., Vol. 26, No. 8, 1987alyst/molar flow of n-heptane fed) was comprised between150 and 6000 kg-s-kmol-l. Before the catalyst was intro-duced into the reactor, this was mixed with glass chips ofthe same particle size in order to keep the volume of thebed constant in all the experiments, and to minimize thethermal effects due to the reaction. Then, the temperaturewas raised to 450 C in Hz flow and was kept a t this tem-perature for 2 h. After this pretreatment, the temperaturewas set to the desired reaction temperature, the hydrogenflow was regulated to obtain a H,/n-heptane molar ratioof 5, and the hydrocarbon flow was started. The reactantswere preheated and then fed to the reactor. The productsof the reactor were cooled, and the liquid fraction wasseparated from the gas fraction and then collected andanalyzed. The liquid products were analyzed by gas-liquidchromatography using a 4.3-m column with silicone gumrubber (SE-30) on Chromosorb P at a temperature pro-gram of 80-170 C. The gas products were analyzed witha 2-m column of silica gel and Porapak Q at temperaturesof 70 and 170 C.Only the experiments with mass balances of 100% 5%were considered. Experiments were repeated to test theexperimental reproducibility.The molar yield curves for different cat/oil (weight ofcatalyst/total weight of n-heptane fed in an experiment)ratios were obtained from the representations, obtainedexperimentally, of the conversion and the molar yield ofa product vs. the time on stream (T.O.S.) at different W/FOratios, by

cat - W 1 1- --oil F0 T.O.S. Mn.heptanewhere M is the molecular weight.Conversion was defined here as he number of n-heptanemoles reacted by each n-heptane mole fed, while the yieldto each product was defined as he number of moles of thisproduct obtained by each n-heptane mole fed and selec-tivity was defiied as he number of moles obtained by eachn-heptane mole reacted.Results and Discussion

Reaction Products and Initial Selectivities. Thereaction products obtained during hydroisomerization andhydrocracking on noble metals (Pt, Pd)/Y zeolite bi-functional catalyts have been largely covered in the lit-erature (Steijns et al., 1981; Weitkamp e t al., 1983; Galleiet al., 1981; Ribeiro et al., 1982; Weitkamp and Ernst, 1985;Giannetto et al., 1985; Weitkamp, 1982; Weitkamp et al.,1984; Jacobs e t al., 1980). However, with non-noble metals(Ni, Mo), detailed work is scarce (Franck and Le Page,1981; Jothimurugesan and Bhatia, 1984; Choudhary andSaraf, 1978).In this work, the molar yields to the different reactionproducts at different levels of conversion have been ob-tained, with a 4 wt Ni0-8 w t % Mo03/HYUS catalyst,by changing the amount of catalyst, and the results, at 350C, are given in Figure 1. In these curves the slope of thetangent, when conversion goes to zero, represents the initialselectivities to the different reaction products (Table I).There we see that the selectivity to branched heptanes is78.5%, the rest of the products being hydrocarbons witha number of carbon atoms lower than seven and which areformed by cracking on acid sites and hydrogenolysis onthe NiO and MOO,, as will be discussed later.Product Distribution in the C, somerized Fraction.In Table I it can be seen that 2- and 3-methylhexane ac-count for -91% of the branching isomers of n-heptane,while the 2/3-methylhexane ratio (at 350 C is 0.76. From

Table I. Initial Selectivit ies to the Different ReactionProducts in the Hydrocracking of II -Heptane with a 4 wt 70Ni0-8 wt M o 0 3 / H W S Catalystinitial selectivity at

350 C 300 Cmethane 0.018 0.001ethane 0.003 0.001propane 0.111 0.026isobutane 0.125 0.027n utane 0.021 0.002butenes 0 0C4 fraction 0.146 0.029isopentane 0.021 0.002n-pentane 0.018 0.003pentenes 0 0C5 fraction 0.039 0.0052-methylpentane 0.015 0.0023-methylpentane 0.008 0.001C6 fraction 0.061 0.019hexane 0.038 0.0162-methylhexane 0.309 0.3963-methylhexane 0.405 0.487other i-C7 0.071 0.053i-C7 fraction 0.785 0.936

Table 11. Thermodynamic Equilibrium Distribution of C,Isomers at 350 Cequilibrium distribution, mol

2-methylhexane 17.233-methylhexane 21.272,2-dimethylpentane 21.192,3-dimethylpentane 26.712,4-dimethylpentane 5.863,3-dimethylpentane 7.75Figure 2 one sees that if the formation of 2- and 3-methylhexane would only take place by protonated cy-clopropanes (PCP) (Weitkamp and Jacobs, 1981), a 2/3-methylhexane ratio of 0.5 should be expected. The ratioobserved experimentally, and which is very close to thethermodynamic equilibrium (see Table 11), indicates thatthe following 1,2-methylshift (Fajula, 1985)

should also take place and is very fast on this catalyst.Furthermore, in Table I it is also shown that the amountof the other branched isomers of n-heptane is quite low,and it is far away from the equilibrium composition (Table11). This result can be a consequence of a lower rate offormation of dibranched prqducts, a faster cracking of thedibranched isomers of n-heptane, or both effects.From the point of view of a PCP mechanism, the isom-erization of monobranched to dibranched heptanes goesthrough secondary and tertiary carbocations (Figure 3) andtherefore it should be thermodynamically favorable.However, it has been found (Baltanas et al., 1983) that therate constant for the formation of multibranched (MTB)isomers of n-octane from monobranched (MB) is 1.5 lowerthan the rate of formation of monobranched isomers fromn-octane. Taking into account this fact and the influenceof the hydrocarbon chain length on the relative rate offormation of mono- and multibranched isomers, we wouldexpect that, in the case of n-heptane, k,TB/kMB 1/2.This factor plus the fact that the isomerization follows onescheme of the type, n-heptane-MB-MTB, and thatwe are considering initial selectivities would explain thelow values of MTB found a t low levels of conversion.

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Ind. Eng. Chem. Res., Vol. 26,No. 8,1987 1497

0 2'i ETHANE10 2 30 LO

A

w i1

10 2 30 LOSOPE N TANE

10

5 E0 2 30 LO

O O 20 30 LO

01

IO 20 LO

IO I

TOTAL CONVERSION ( I0 3 PENTENESt

10 20 33 40

1 O 3MPENTANE5 EI O 2 30 d o

2 MHEXANE- 10>

5

IO 20 30 40OTHERS i-C7

2MPENTANE

HEXANE

0.5 o p

IO 20 30 LO

10 20 30 40

TOTAL CONVERSION ( * /e)Figure 1. Selectivity plots for products obtained during hydro-cracking of n-heptane on a 4 wt Ni0-8 wt MoOa/HYUS cat-alyst , a t 350 OC. Cat/oil ratios (weight of catalyst/ total weight ofn-heptane fed in an experiment): 0)1.2 X 0) X A)3 x 10-3.On the other hand, it is expected that MTB isomerscrack faster than the MB ones (Baltanas et al., 1983;Steijns and Froment, 1981). Indeed, from Figure 4, wherethe different cracking possibilities involvingon y secondaryand tertiary carbonium ions are presented, it can be seen

L m3 2MHexane

3M Hexane

2 MHe a n eFigure 2. Formation of 2-methylhexane and 3-methylhexane fromC7 carbocations through PCP intermediates.+ .3DM Pentane

ZZDMRnlaneand 3Elhylpenlane

2,PDMPcntane /) ' - and9E l h y l p cn tane2,ZDMPentan

3Methylhexane - Nbranched2Mr th y l h cxane Di branchedFigure 3. Formation of dibranched isomers from 2-methylhexaneand 3-methylhexane through PCP intermediates.that the MB isomers always crack through a C-typemechanism (secondary-econdary carbocation), while theMTB can also crack through the more probable B1 andB2 mechanism (secondary-tertiary and tertiary-secondarycarbocations, respectively; see Figure 4) (Weitkamp et al.,1983). All this is reflected in the cracking products ob-tained (Table I),which show that the C4 fraction is mainlyformed by isobutane, which can only be formed by crackingof 2,2 - and 2,4-dimethylpentane through a B1 and B2mechanism, respectively.Product Distribution in the Cracked Fraction. Theformation of methane as a primary product is difficult toexplain by an acid-catalyzed mechanism if we take intoaccount that t he production of methane involves primarycarbonium ions and, moreover, no methane is observed asa primary product when the reaction is carried out on thepurely acid H W S zeolite (Corma et al., 1984). Therefore,we believe that, in this system, methane could be formedby hydrogenolysis on the metal part of the catalyst, whilewhen catalysts containing noble metals are used, methaneis not observed (Weitkamp et al., 1983; Weitkamp andErnst, 1985; Jacobs et al., 1980; Martens et al., 1985).

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1498 Ind. Eng. Chem. Res., Vol. 26, No. 8, 1987

2 MHe xa n e I

AMHexane

A * A + A2,2 DMPentane A

2,3 DMPentane

2J DMPentane

AFigure 4. Cracking possibilities of the monobranched and di-branched C, isomers, involving only secondary and tertiary carbo-nium ions.

The isobutaneln-butane ratio can be taken as an indi-cation of the relative rate of cracking by B (Bl,B2) andC mechanisms (see Figure 4). If this is so, then by com-paring the isobutaneln-butane ratio observed at 300 and350 C reaction temperatures (Table I), it is obvious thatthe cracking through mechanism type C (formation ofn-butane) has a higher apparent activation energy thancracking through mechanisms of type B (B1 and B2, re-sponsible for the formation of isobutane). This conclusionwould agree with the structures involved in those mecha-nisms and also with previously reported results (Cormaet al., 1985; Weitkamp e t al., 1983).Another interesting feature which can be observed in theresults of Table I is that the c6 + C5+ C4/C1+ C2+ C3ratio is higher than 1. This result indicates that t he C6,C5, and C4 fractions are not only produced by cracking orhydrogenolysis of C7 but also by other reactions involvingconsecutive alkylation-cracking processes, as has beenobserved during cracking of alkanes on Y zeolites (Boltonand Bujalski, 1971; Weisz, 1970; L6pez Agudo et al., 1981).On the other hand, when hydrocracking is carried out onPt or Pd/HYUS zeolite catalysts, the product distributionis perfectly symmetrical with respect to the number ofcarbons in the products (Weitkamp et al., 1983). From thispoint of view, the Ni-Mo/HYUS catalysts present an in-termediate behavior between that of a monofunctionalcracking HYUS zeolite catalyst and an ideal bifunctionalPt/ HYUS catalyst. This can be due to the lower hydro-genating activity of the Ni-Mo with respect to the noblemetals. The consequence of this lower hydrogenationcapacity is the presence of small amounts of olefins in theproducts, never detected on P t / H W S catalyst, which, onthe other hand, are the origin of the consecutive alkyla-tion-cracking reactions observed in the Ni-Mo/HYUScatalyst.

0 5 t AO 3 t

i l1CARBON NUMBER OF CRACKED PRODUCTS

Figure 5. Selectivity of the different cracking fractions at 350 Cfor catalysts with Ni/(Ni + Mo) atomic ratio: 0), 0) .248, v)0.441, 0 )0.50, W) 0.539, A) .569, A) .0.HYDROGEWLYSIS CRACKING ISOMERIZATION

2 p,

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Ind. Eng. Chem. Res., Vol. 26, No. 8, 1987 1499l L O r A

150

_j[00 3 1100

2o tL o y e---01 2 0 3 4 05 06 ION i / N i + M o ( a t o m i c r a t i o /

Figure 7. Variation of the initial n-heptane reaction rate vs. theNi/(Ni + Mo) atomic ratio of the catalyst: 0)00 OC, 0)30 OC,A) 50 O C reaction temperatures.

Ni /N i + Mo ( a tomlc ra t l o )Figure 8. Intensity of the Bronsted band for catalystswith differentNi/(Ni + Mo) atomic ratio. Temperature desorption of pyridine:0)50 c, 0)50 c, A) 50 c.

acidity for the different catalysts, measured by pyridineadsorption-desorption (1550-cm-l band frequency), s givenin Figure 8. Comparing both figures it can be concludedthat there is not a direct relation between the activity andthe acidity of the Ni-Mo/HYUS catalysts studied. Adirect relation is found however when considering only thesamples with a Ni /(Ni + Mo) 0.5 (Figure 9). Theseresults would be in agreement with a previous work(Vbquez et al., 1986), which presented, on the basis ofkinetic data, that for Ni/(Ni + Mo) < 0.44-0.5, the con-trolling step of the hydrocracking is the dehydrogenationof n-heptane on the metal, while for samples with Ni/(Ni+ Mo) 0.5 the reaction of carbonium ion on the acidcenters is the controlling step.In conclusion it can be said that on a 4wt Ni0-8 wtMo03/HYUS catalysts, the 1,2-methyl shift reactionis very fast and the 2/3-methylhexane ratio observed ex-perimentally is very close to the thermodynamic equilib-rium. On the other hand, according to the cracked fractiondistribution, the dibranched isomers crack preferably tothe monobranched ones. The formation of methane as aprimary product could be explained by hydrogenolysis inthe metal part of the catalyst. This fact and the nonsym-metric distribution found in the cracked products indicatethat the Ni-Mo/HYUS catalyst presents an intermediatebehavior between that of a monofunctional cracking H W Szeolite catalyst and an ideal bifunctional Pt/HYUS cata-

I 2 3

' 1550cm-1 a uFigure 9. Relation between the initial n-heptane reaction rate(activity) and the Bronsted band intensity for catalysts with a Ni/(Ni + Mo) atomic rat io 0.5.lyst. The inital selectivities for hydrogenolysis, cracking,and isomerization vary as a function of the Ni/(Ni + Mo)ratio of the catalyst. Finally, a direct relation is foundbetween activity and acidity for catalysts with Ni/(Ni +Mo) 0.5.

Registry No. Ni, 7440-02-0; Mo, 7439-98-7; H3C(CH2),CH,,142-82-5; CHI, 74-82-8; HSCCH, 74-84-0; H&CH2CH3,74-98-6;(H,C)2CHCH,, 75-28-5; H,C(CH2)2CH,, 106-97-8; (H&)&HC-H2CH3, 78-78-4; H&(CH2)3CH3,109-66-0; (H3C)*CH(CH,)&H,,107-83-5; H&CH&H(CH,)CH,CH,, 96-14-0; H&(CH2),CH3,110-54-3; butene, 25167-67-3; pentene, 25377-72-4; 2-methylhexane,591-76-4; 3-methylhexane, 589-34-4; 2,2-dimethylpentane, 590-35-2;2,3-dimethylpentane, 565-59-3; 2,4-dimethylpentane, 108-08-7;3,3-dimethylpentane, 562-49-2.Litera ture CitedBaltanas, M. A,; Vansina, H.; Froment, G. F. Ind . Eng . Chem . Prod .Res. Deu. 1983, 22, 531.Bolton, A. P. Zeoli tes Chemistry and Catalysis; Rabo, J., Ed., ACSMonograph Series 171; American Chemical Society: Washington,DC. 1976; p 714.Bolton, A. P.; Bujalski, R. L. J . Cata l . 1971, 23, 331.Coonradt, H. L.; Garwood, W. E. Ind . Eng. Che m. Process Des. Deu.Corma, A.; Mo nth, J. B.; Orchill&, A. V. Ind . Eng. Ch em. Prod. Res.Corma, A.; Planelles, J. H.; Tomls, F. J . Catal . 1985, 97, 445.Chen, N. Y.; Gorring, R. L; Ireland, H. R.; Stein, T. R. Oil Gas J .Choudhary, N.; Saraf, D. N. Ind . Eng . Chem. Prod . Res . Deu . 1978,Fajula, F. S t u d . Surf Sci. Catal . 1985, 20, 361.Franck, J. P.; Le Page, J. F. Proc. Int. Congr. Catal., 7th 1981,792.Gallei, E.; Marosi, L.; Schwarzmann, M.; Lorenz, E. US. PatentGiannetto, G.; Perot, G.; Guisnet, M. S t u d . Surf Sci. Catal . 1985,Guisnet, M.; Perot, G. NAT O ASI Ser., Ser. E 1984,80, 397.Haynes, H. W., Jr. ; Parcher, J. F.; Helmer, N. E. I n d . E n g . C h e m .Jacobs, P. A.; Uytterhoeven, J. B.; Steyns, M.; Froment, G.; Weit-Jothimurugesan, K.; Bhatia, S. Can. J . C h e m . E n g . 1984, 62, 390.Ldpez Agudo, A.; Asensio, A.; Corma, A. J . Cata l . 1981, 6 9 , 274.Martens, J.;Weitkamp, J.; Jacobs, P. A. S t u d . Surf Sci. Catal . 1985,Mooi, J. US . Patent 4238316, 1980.Ribeiro, F.; Marcilly, C.; Guisnet, M. J . Catal . 1982, 78, 267.Steijns, M.; Froment, G. F. Ind . E ng . C hem. Prod . Res . Deu . 1981,20, 660.Steijns,M.; Froment, G. F.; Jacobs, P.; Uytterhoeven,J.; Weitkamp,J. I n d . E n g . C h e m . Prod. Res. Deu. 1981, 20, 654.Ternan, M.; Parson, B. I. U.S. Paten t 4 176 051, 1979.Vtizquez, M. I.; Escardino, A.; Aucejo, A.; Corma, A. Can. J . C h e m .Ward, J. W. US . Pa tent 3926780, 1975.Ward, J. W. Preparat ion of Cata lys t I l l ; Poncelet, G., Grange, P.,Weitkamp, J. I n d . E n g . C h e m . Prod. Res . Deu . 1982, 21, 550.Weitkamp, J.; Ernst, S. Stud Surf Sci. C ata l . 1985, 20, 419.

1964, 3(1), 38.Deu. 1984,23(3), 404.

1977, 75 , 165.17(3), 196.

4 252 688, 1981.20, 265.Process Des. Deu. 1983, 22, 401.kamp, J. Proc. I n t . C o n f . Z e o l it e s , 5 t h 1980, 607.

20, 427.

E n g . 1986, 64 272.Jacobs, P., Eds.; Wiley: New York, 1983; p 587.

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1500WeitkamD. J.: Jacobs. A. PreDr.-Am. Chem. SOC . iu. Pet. Chem.

I n d . Eng. Chem. Res. 1987, 26 1500-1505Weisz. P. B. An nu. Rev. Phvs. Chem. 1970,21, 175.1981, i6 9.

28, 279.Weitkamp, J.; Jacobs, P. A,; Ernst, S. S tud . Sur f . Sci. Catal. 1984,Weitkamp,J.;Jacobs,P. A.; Martens, J. A. App l. Catal. 1983,8, 123.Received for review Jun e 16, 1986Revised manuscript received March 31, 1987Accepted April 30, 1987

Cobalt Mixed Spinels as Catalysts for the Synthesis ofHydrocarbons?

Giuseppe Fornasari, Stefan0 Gusi, Ferruccio Trifirb,* and Angelo VaccariDipar t imento d i C himica Zndustria le e dei Materiali , Viale Risorgim ento 4 40136 Bologna, I ta lyTh e nat ure and the catalyt ic activity in the Fischer-Tropsch synthesis of cobalt, copper, zinc, andchromium mixed oxides have been investigated for a wide range of compositions. Most of theprecursors showed a hydrotalcite-like structure and formed by calcination essentially a spinel-typephase (notwithstanding the high values of the M(II)/M(III) ratio (M = metal)). For all catalyststhe hydrocarbons were the main products and presented typical Schulz-Flory distributions. Whilethe Co/Cr catalysts showed very low activity, a maximum was obtained for catalysts containingcomparable amounts of copper and cobalt. In all samples a spinel-type phase was present afterreaction, while the formation of metallic cobalt and /or cobalt oxides was not observed. On the otherhand, metallic copper after both reduction and reaction was detected by N 2 0 itrations. The catalyticactivi ty was att ributed to a synergetic effect between copper and cobalt, correlable to the presenceof a nonstoichiometric spinel-type phase or to an interaction between this phase and the well-dispersedmetallic copper formed in reducing conditions.

The production of chemical feedstocks or fuels fromsyngas became an attractive alternative to petroleumsupplies. The synthesis of hydrocarbons, with the excep-tion of methane, is commonly referred to as the Fischer-Tropsch reaction and is now utilized on a large scale in theSouth African Sasol plants.Many excellent books and reviews have been published,also recently, which give detailed information about thedifferent aspects of this reaction (Storch et al., 1951; Pi-chler, 1952; Anderson, 1956; Vannice, 1976; Biloen andSachtler, 1980; Dry, 1981; Rofer-De Poorter, 1981; Hen-rici-0liv8 and Oliv8, 1984).Groups 8-10 transition metals or their alloys, supportedor unsupported, have always been employed as catalysts,and different preparation techniques have been used(Frohning, 1977; Dry, 1981); however, to achieve a highlydispersed metal surface, a reduction pretreatment mustbe performed, whatever the preparation method (Storchet al., 1951; Pichler, 1952; Anderson, 1956; Clarke et al.,1962, Dry, 1981). Historically, the first metals to be usedwere iron and cobalt, alone or alloyed together (Sabatierand Senderens, 1902; BASF, 1913; Fischer and Tropsch,1923; Pichler, 1952), since nickel showed activity towardmethanation only (Sabatier and Senderens, 1902), hodiumsharply shifted the selectivity toward oxygenated com-pounds (Dry, 1981), and P d, Os, Ir, and Pt were found tohave low activities (Pichler, 1952; Vannice, 1976, 1977).Ruthenium has the higher overall activity, giving rise tothe formation of waxy fractions, but the methanation re-

* To whom correspondence should be addressed.In this pa per th e periodic group notation is in accord withrecent actions by IUPAC and ACS nomenclature committees. Aand B notation is eliminated because of wide confusion. GroupsIA and IIA become groups 1 and 2. The d-transition elementscomprise groups 3 through 12, and the p-block elements comprisegroups 13 through 18. (Note that the former Roman numberdesignation is preserved in the last digit of the numbering: e.g.,I11- and 13.)0888-5885/87/2626-1500 01.50/0

action is the most favored (Pichler, 1952; Vannice, 1977).Many efforts have been successfully made to improveRu-based systems (Vannice, 1975; Dalla Betta and Shelef,1977; King, 1978 Everson e t al., 1978; Gonzales and Miura,1982).Among the carriers, the most commonly used are SO2,Kieselguhr, and A1203;however, some authors have de-veloped zeolite-supported systems (Jacobs, 1980; Nijs etal., 1980; Naccache and Ben Taari t, 1980; Peuckert andLinden, 1984; Leith, 1983). While the supports are to beconsidered physical promoters because of their high surfacearea, chemical promoters such asNi, Zr, Mn, and Cu (Dry,1981; van Dijk and van der Baan, 1982; Bruce et al., 1983)or alkaline oxides, which partially neutralize the acidityof the supports (Fischer and Tropsch, 1930; Dry, 1981),have been widely employed.Recently, cobalt- and nickel-containing catalysts havebeen proposed as active also in the higher alcohols syn-thesis (Courty et al., 1982, 1983; Fujimoto and Oba, 1985;Uchiyama et al., 1985). In particular, the catalysts de-veloped at the Institute FranGais du Petrole (IFP) havecompositions corresponding to that of alkalized conven-tional copper-based methanol synthesis catalysts modifiedby the addition of cobalt.In this research the catalytic activity of Co, Cu, Zn, andCr mixed oxides was investigated for a wide range ofcompositions, with the aim to study the catalytic behaviorof the nonmetallic cobalt and the role of the other elementsadded.In previous works, it was shown that hydrotalcite-likephases [HY, having general formula M1I6MI1I2-(OH)&03.4H20] may be useful precursors of catalysts forthe synthesis of methanol a t low temperature (Gherardiet al., 1983; Gusi et al., 1985). In these precursors allcations are randomly distributed in positively chargedbrucite-like layers alternated with negatively charged(C03.4H20)2-nterlayers (Busetto et al., 1984). Therefore,we tried to prepare catalysts with different relative ratiosof Co, Cu, Zn, and Cr starting from homogeneous pre-

1987 American Chemical Society