Derived Bimetallic Catalysts

Studies of Mixed-Metal Cluster-Derived Catalysts 

Advances using EXAFS coupled with Mossbauer spectroscopy have given better insight into the location, coordination shell, and oxidation states of multimetallic ensembles on supporting oxides. Still, relatively little is known at present about the actual shapes and structures of the mixed metal species resulting from the thermal decomposition of the precursor clusters. In particular, the extent to which the original cluster framework, metal composition, and ligand coordination is maintained is unclear. 

The surface reaction of impregnated mixed metal cluster complexes may be analogous to that of homometallic clusters on hydrated and dehydrated metal oxides as described in Sections III and IV. Bimetallic clusters are converted to anionic surface species by simple deprotonation via 0 on dehydrated MgO or AI2O3 surfaces these species have been characterized by IR spectroscopy (119). The ionic interaction with surface cations such as AF and Mg is demonstrated by IR and NMR measurements. The surface polynuclear carbonyl anions are stable up to about 373 K. If heated in vacuo at higher temperature, extensive decomposition takes place to give a mixture of Ru (or Os) metal particles and Fe oxides, accompanied by the evolution of H2, CO, and CO2. 

The resulting HOs3(CO)n(OSi=) species is converted to mononuclear osmium carbonyl species (Vco 2120,2040, and 1975 cm ) at elevated temperatures, similar to the decomposition of Os3(CO)i2 on silica. H2RuOs3(CO),3 on alumina is also decomposed on heating to form Ru(CO)2 and HOssfCO), fragments, which are eventually converted to a mixture of Os and Ru ensembles segregated from each other. It was demonstrated by IR spectroscopy 

In this context, when a physical mixture of Fe3(CO)i2 and Ru3(CO)i2 [or Ru3(CO)i2 and Os3(CO)i2] is impregnated on silica (or alumina), no significant interaction occurs between the carbonyl clusters. It was suggested that heating the sample in an H2 or He atmosphere at 420 K results in physically mixed carbonyl and as yet uncharacterized particles. 

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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]. 

Laboratory-scale liquid phase oxidation with heterogeneous catalysis is generally performed under mild conditions by bubbling air or oxygen at 20-50 C and atmospheric pressure in the presence of Pd, Pt, Au, or derived bimetallic catalysts [4]. 

Wang YX, Balbuena PB. 2005a. Design of oxygen reduction bimetallic catalysts Ab-initio-derived thermodynamic guidelines. J Phys Chem B 109 18902-18906. 

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... 

Using the dendrimer route, it is possible to prepare supported catalysts not available via traditional routes. Dendrimer derived Pt-Au catalysts having compositions within the bulk miscibility gap can be prepared on several oxide supports. For all the supports studied, the bimetallic catalysts exhibited synergism with respect to mono- and cometallic catalysts for the CO oxidation and hydrocarbon NOx SCR reactions. The bimetallic Pt-Au catalysts also showed evidence of exchanging surface and subsurface atoms in response to strongly binding ligands such as CO. 

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. 

Triazole derivatives could be synthesized from different starting substrates. Various triazoles 155 were synthesized from nonactivated terminal alkynes 152, allyl methyl carbonate 153 and trimethylsilyl azide 154 in a [3 + 2] cycloaddition with the use of the Pd(0)-Cu(I) bimetallic catalyst <03JA7786>. The allyl group of 155 was efficiently deprotected by ruthenium-catalyzed isomerization followed by ozonolysis to give 4-substituted triazoles 156. a-Aminoacetophenones 157 were reacted with hydrazines in acetic acid to give an efficient... 

Inspired by the bimetallic catalyst developed by Shibasaki and coworkers with 2 1 complexes of BINOL with aluminum, Manickam and Sundararajan prepared 2 1 complexes of the aminodiol 420 with aluminum [87,88]. Reaction of malonate esters with cyclopentenone or cyclohexenone results in asymmetric induction of at least 90 % ee with dibutyl malonate, as detailed in Sch. 57. A catalyst prepared by the reaction of 2 equiv. diol 419 with lithium aluminum hydride was found to result in asymmetric induction for the reaction of cyclohexenone with malonate 390d similar to that observed with the catalyst derived from 420 and from BINOL, although the rate was slightly slower. 

Carbonyl-derived RhCo bimetallic catalysts exhibit high selectivity toward skeletal rearrangement of methylcyclopentane (MCP) (to a mixture of 2- and 3-methylpentanes), whereas on the conventional counterpart hydrocracking... 

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

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 understanding of the interaction of S with bimetallic surfaces is a critical issue in two important areas of heterogeneous catalysis. On one hand, hydrocarbon reforming catalysts that combine noble and late-transition metals are very sensitive to sulphur poisoning [6,7]. For commercial reasons, there is a clear need to increase the lifetime of this type of catalysts. On the other hand. Mo- and W-based bimetallic catalysts are frequently used for hydrodesulphurization (HDS) processes in oil refineries [4,5,7,8]. In order to improve the quality of fuels and oil-derived feedstocks there is a general desire to enhance the activity of HDS catalysts. These facts have motivated many studies investigating the adsorption of S on well-defined bimetallic surfaces prepared by the deposition of a metal (Co, Ni, Cu, Ag, Au, Zn, A1 or Sn) onto a single-crystal face of anodier metal (Mo, Ru, Pt, W or Re) [9-29]. 

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. 

In the presence of the sodium-containing heterobimetallic catalyst (R)-LSB (10 mol%), the reaction of enone 52 with TBHP (2 equiv) was found to give the desired epoxide with 83% ee and in 92% yield [56]. Unfortunately LSB as well as other bimetallic catalysts were not useful for many other enones. Interestingly, in marked contrast to LSB an alkali metal free lanthanoid BINOL complex, which was prepared from Ln(0- -Pr)3 and (R)-BINOL or a derivative thereof (1 or 1.25 molar equiv) in the presence of MS 4A (Scheme 17), was found to be applicable to a range of enone substrates. Regarding enones with an aryl-substitu-ent in the a-keto position, the most effective catalytic system was revealed when using a lanthanum-(.R/)-3-hydroxymethyl-BINOL complex La-51 (l-5mol%) and cumene hydroperoxide (CMHP) as oxidant. The asymmetric epoxidation proceeded with excellent enantioselectivities (ees between 85 and 94%) and yields up to 95%. 

Arenes undergo couphng with ArSnCls in the presence of a bimetallic catalyst of PdCl2 and CuCl2. An oposition of iV,iV-dimethylbenzylamines is also activated toward coupling with acryhc acid derivatives. ... 

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