Bimetallic catalysts, cluster-derived

Molecular precursors for tailored metal catalysts, 38 283-392 see also Bimetallic catalysts, cluster-derived Zeolites carbon-supported, 38 389-390 chemical interaction between clusters and supports, 38 295-296... 

This set of results suggests that bimetallic carbonyl clusters derived from mixed Fe/Rh cluster complexes yield discrete RhFe atom sites that are active for olefin hydroformylation as well as for successive hydrogenation of these products to alcohols. Enhancement of hydroformylation over simple hydrogenation of olefins on the Fe-containing Rh cluster-derived catalysts results in an appreciable improvement in oxygenate selectivity. 

Fig. 25. Carbon efficiencies of oxygenated products in the CO + H2 reaction and ethanol selectivities on bimetallic RhCo cluster-derived catalysts impregnated on Zr02 (0.2 wt% metal) (CO/H2 ratio 20/45 cmHg, 200°C). O.C. represents oxygenated products on a carbon basis.

A MgO-supported W—Pt catalyst has been prepared from IWsPttCOIotNCPh) (i -C5H5)2l (Fig. 70), reduced under a Hs stream at 400 C, and characterized by IR, EXAFS, TEM and chemisorption of Hs, CO, and O2. Activity in toluene hydrogenation at 1 atm and 60 C was more than an order of magnitude less for the bimetallic cluster-derived catalyst, than for a catalyst prepared from the two monometallic precursors. 

The study of propylene hydroformylahon reaction over the above-mentioned cluster-derived bimetallic catalysts showed that their activity followed the trend FeRhs < FeRh4 < Fe2Rh4 > Fe3Rh2. Moreover, hydroformylahon activity of these bimetallic systems was higher than that of the catalysts prepared by co-impregnahon using monometallic Rh and Fe carbonyl precursors in the same Rh/Fe metal ratios ]192]. 

Shephard, D. S., Maschmeyer, T., Sankar, G., Thomas, J. M., Ozkaya, D., Johnson, B. F. G., Raja, R., Oldroyd, R. D. and Bell, R. G. Preparation, characterization and performance of encapsulated copper-ruthenium bimetallic catalysts derived from molecular cluster carbonyl precursors, Chem. Eur. J., 1998, 4, 1214-1224. 

Table XV gives a summary of some bimetallic catalysts derived from the different bimetal clusters supported on metal oxides and applications to catalytic reactions.

Mossbauer Parameters Hi-Reduced RhFe, PlFe, and PdFe Bimetallic Cluster-Derived Catalysts"... 

CO dissociation but also for CO insertion. A similar promotion mechanism was previously proposed for RhFe and PdFe carbonyl cluster-derived catalysts which exhibited substantial improvement in C1-C2 alcohol production in CO hydrogenation. The conventional IrFe catalysts prepared from coimpregnation of IrCl4 and FeCls provided poor yield and selectivity toward alcohols versus the corresponding cluster-derived catalysts. The bimetallic IrFe cluster precursors offer the advantages of higher metal dispersion and more uniform distribution of active IrFe sites over the conventional salt-derived catalyst preparation. 

However, only alkyl formates are formed in the conventional reactions of alcohols, CO2 and H2 using transition metal complexes, because intermediary hydride complexes generally react with CO2 to give formate complexes. On the other hand, we have found that mthenium cluster anions effectively catalyze the hydrogenation of CO2 to CO, methanol, and methane without forming formate derivatives [2-4]. Ethanol was also directly formed from CO2 and H2 with ruthenium-cobalt bimetallic catalyst [5]. In this paper, we report that this bimetallic catalytic... 

The effect of catalyst composition on the selectivity to the desired CDE is remarkable. It is clear that monometallic cluster catalysts almost completely hydrogenate CDT to CDA, whereas all three bimetallic clusters (RuSn, RhSn, and PtSn ) exhibit high selectivity toward CDE at approximately the same CDT conversion (50-75%). Pure tin clusters derived from Ph SnH are poor catalysts both in terms of activity and selectivity (conversion less than 10%). 

Elements for the deposition of heterobinuclear complexes for preparing bimetallic catalysts have been reported by Ichikawa [48]. The use of heterobinuclear complexes as precursors for bimetallic catalysts was aimed at the fine-tuned control of a homogeneous composition in the nuclearity of bimetallic particles. As compared to catalysts prepared by NSD methods, mixed-metal cluster-derived catalysts should retain more bimetallic ensembles. However, the use of heterobinuclear complexes is limited by the availability of high-nuclearity clusters and by the narrow choice of metallic couples. The different types of interaction of these complexes with the support are the same as previously described for the NSD methods. 

A supported bimetallic catalyst derived from the sulfido cluster [Mo2Co2(j 4-S)( /3-S)2Cp2(CO)4] (10) has been studied in CO methanation. It was suggested that the clusters do not fragment and re-aggregate into larger crystallites. ... 

Heterogeneous, alumina-supported bimetallic catalysts derived from the sulfido clusters [Mo2Ni2S4Cp4] and [Mo2Ni2S4Cp2(CO)2] have been studied in CO metha-... 

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