Bimetallic catalysts preparation

Del Angel, P. et al., Aggregation state of Pt-Au/C bimetallic catalysts prepared by surface redox reactions, Langmuir, 16, 7210, 2000. 

J. Margitfalvi, S. Szabo, andF. Nagy, Supported bimetallic catalysts prepared by controlled surface reactions. Stud. Surf. Sci. Catal. 27, 373-409 (1983). 

In bimetallic catalysts prepared by catalytic reduction of copper by hydrogen, copper is deposited as three-dimensional agglomerates which are located, at low copper loadings, on the edges, corners, and rims of the parent metallic particles. The mechanism of deposition can be transferred from that proposed in corrosion and involving a local electrochemical cell ... 

In conclusion, redox reactions allow the surface to be tailored during catalyst preparation, which explains the exceptional catalytic properties, particularly in terms of selectivity, of bimetallic catalysts prepared by these techniques. 

A bimetallic catalyst prepared from BINOL and lithium aluminum hydride has been found to result in useful asymmetric induction in the Pudovik reaction [17]. The (f )-ALB catalyst 64 (10 mol %) facilitates the addition of dimethyl phosphite to a variety of electron-rich and electron-poor aryl aldehydes in high yield with induction in the range 71-90 % ee. The nature of the solvent is important in this reaction—the induction for addition to benzaldehyde dropped from 85 % ee to 65 % ee when the solvent was changed from toluene to dichloromethane. Aluminum seems to be a key to the success of this reaction, because reaction with benzaldehyde was not as successful with other bimetallic catalysts. BINOL catalysts with lanthanum and potassium gave only 2 % ee, a catalyst with lanthanum and sodium gave a low 32 % ee, and a catalyst with lanthanum and lithium gave only a 28 % ee [18]. Aliphatic aldehydes were not successfully hydrophosphonylated with dimethyl phosphite by catalyst 64 (Sch. 9). Induction was low (3-24 % ee) for unbranched and branched substrates. a,/3-Unsaturated aldehydes were, however, reported to work nearly as well as aryl aldehydes with four examples in the range 55-89 % ee. The failure of aliphatic aldehydes with this catalyst can be overcome by reduction of the product obtained from reactions with a,)3-unsaturated aldehydes. As illustrated by the reduction of 67 with palladium on carbon, this can be done without epimerization of the a-hydroxy phos-phonate. 

Guczi, L., Stefler, G., Borko, L., Koppany, Z., Mizukami, F., Toba, M., and Niwa, S. Re-Co bimetallic catalysts prepared by sol/gel technique Characterization and catalytic properties. Applied Catalysis. A, General, 2003, 246, 79. 

Pt-Au/Al203 bimetallic catalysts prepared by the redox method. 

The final catalysts were activated by either calcination-reduction or drying-reduction of precursors. Two levels of reduction temperature, 573 and 773 K, were chosen. Thus, the denomination of a catalyst reflects composition and preparation method (A/I=monometallic adsorbed/impregnated and CA/CI=bimetallic coadsorbed/coimpregnated catalysts), pretreatment procedure (C=calcination or D=drying) and activation temperature (5 = 573 K or 7 = 773 K), e.g. CAC7 denominates the bimetallic catalyst prepared by coadsorption, calcinated and then reduced at 773 K. 

The use of bimetallic catalysts in hydrocarbon reactions have extensively been studied because increased activity, selectivity and stability of the catalyst can be attained with the addition of a second metal. The disadvantage of studying catalytic phenomena on bimetallic catalysts prepared by a conventional coimpregnation method is that the catalyst surfaces are often heterogeneous, which makes it difficult to the catalytic systems. The use of bimetallic clusters as precursors has great advantages for preparation of relatively uniform bimetallic reaction sites well dispersed on oxide surfaces. 

A patent from Monsanto [100] disclosed the oxidation of alkaline solutions of amino alcohols and poly(ethylene glycol) in the presence of bimetallic catalysts prepared by deposition of copper on the surface of platinum. High yields to the corresponding carboxylates were reported. 

For bimetallic catalysts prepared from lowly dispersed parent, no noticeable evolution was pointed out from different CO adsorbed species indicating a non... 

In the field of organic chemistry, the main applications using bimetallic catalysts prepared by surface redox reactions were for selective hydrogenation and hydrogenolysis reactions. 

By FTIR of adsorbed CO, a preferential deposit of Cu on Pd sites of lower coordination was observed on the bimetallic catalysts prepared by the redox reaction. 

As a recent progress on chiral aluminum Lewis acids, chiral Al(salen) complexes (25) developed by Jacobsen s group were found to be one of the most useful asymmetric catalysts for enantioselective 1,4-addition to a,P-unsaturated carbonyls (Figure 6.4) [110]. Jha and Joshi also reported the Al-Na bimetallic catalyst prepared from SALEN and Red-Al for Michael addition of malonic diesters to cyclic enones. [Ill]... 

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