Bimetallic cluster derived

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. 

Two bimetallic clusters derived from [Ru6C(CO),6]2- have been prepared, in which eight and thirteen metal atoms are present. The reaction of Cu(MeCN)JBF4 with 18 results in the addition of two copper vertices to the Ru6C core [Eq. (14)] (50). 

In this investigation we concentrate on two systems of bimetallic clusters derived from well-defined carbonylated precursors RU 2Cu4C2Cl2(CO)32 and Pd6Ru6(CO)24, for which detailed experimental data are available in the literature [3,4]. 

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

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... 

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. 

Heterogeneous Catalysts Derived from Bimetallic Cluster Compounds... 

It is not currently possible to model the full thermal decomposition of a large number of carbonyl ligands from relatively large bimetallic clusters followed by the subsequent electronic and atomic relaxation using only DFT. To attempt to smdy metal clusters derived from organometallic precursors therefore, we need a rapid approximate method for generating plausible models of the final denuded state of the clusters. 

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

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. 

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. 

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.

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