Bimetallic formulation

The introduction in catalysis of bimetallic formulations created an important area of application of microanalysis in transmission electron microscopy. In particular, with selective hydrogenation and postcombustion catalysts, where the metallic particle sizes are several nanometres, the STEM can be used to determine the composition particle by particle and thus confirm the success of the preparation. Figure 9.16 shows the analysis of individual particles in a bimetallic preparation. It is easy to detect the existence of genuinely bimetallic particles and others containing only platinum. It should, however, be noted that this analysis, obtained on a few nanometer sized particles, concerns only a very small quantity of the catalyst (in the present case approximately 10" g of metal ). As we have noted, it is dangerous to extrapolate only one result of this type to the solid as a whole. A statistical analysis of the response of a very large number of particles, in addition to a preliminary study of the chemical composition at different scales, can be used to confirm that this case indeed concerns two groups of particles. 

Although some of these systems, such as Co-MOR or Fe-ZSM-5, " as well as others, such as pillared-clay-based, appear to have interesting properties, they appear to lack stability in the presence of water and sulfur containing streams after prolonged use. In contrast, it has been shown that bimetallic formulations such as In-Co supported on specific zeolites are highly active and stable in the presence of steam. °... 

An important class of industrial catalysts consists of an active component dispersed in the form of very small particles over high surface area solids. As the field of industrial heterogeneous catalysis has developed, catalyst formulations have evolved such that state-of-the-art catalysts often contain two or more metals and/or main group elements. The additives may promote a desired reaction, prevent undesirable side reactions, or enhance catalyst longevity.Bimetallic nanoparticle catalysts in particular are widely... 

In the search for catalyst formulations superior to PtRu, many alternative Pt binary alloys have been investigated. In recent years, strong interest in PtOs alloys and bimetallics has been shown. Although Os does promote MeOH oxidation on Pt, it is somewhat less active than Ru, apart from high overpotentials (>0.50 V), where Os is less susceptible to overoxidation compared to... 

Alternative catalyst formulations for methane ATR based on bimetallic catalysts have been studied, aiming at increasing the activity of nickel catalysts by the addition of low contents of noble metals. 

The insertion of various isocyanates into chromium(lll) alkoxide M—O bonds has been reported.737 The complexes are prepared by refluxing the isocyanates with a suspension of the alkoxide in benzene. No structural data were given for the products. Unusual bimetallic alkoxides have recently been prepared738 by the reaction of Cr[Al(OPr )4]3 with alcohols and acetylacetone (166). A wide range of spectroscopic methods were used to study them. In general, the results were in accord with a monomeric formulation similar to (166) below Cr[Al(OMe)4]3 was grossly insoluble the small size of the methyl groups may permit extensive polymerization. 

Past efforts in developing coal liquefaction catalysts have focused on alumina-supported systems and, except for exploratory studies, little attention has been given to systematic development of novel formulations. A particularly promising approach to the development of new catalysts specifically designed lor coal liquefaction processes lies in the formulation of multicomponent systems that, in comparison to work on single or bimetallic systems, are essentially unexplored. Use of multimetallic systems offers the possibility of multifunctional catalysts that are needed to perform the many different reactions encountered in coal processing. Because of its versatility for the preparation of multimetallic catalysts, the HTO system is an excellent candidate for further development. 

Metal alkylidyne fragments are frequently invoked as intermediates in the transformation of hydrocarbons on metal surfaces. These species are usually formulated as triply bridging alkylidynes however, terminal surface alkylidynes may be considered as reactive surface intermediates (30). Evidence for metal carbyne intermediates on Pt—Co bimetallic surfaces was found in a study of the isomerization and hydrogenolysis of alkanes (3]). 

The total capacity of the semiregenerative units exceeded 5.0 million b/d while CCR units reached 3.8 million b/d. The simultaneous use of CCR technology and bimetallic catalysts has given UOP a unique position in the field of catalytic reformer process licensing. Recent catalyst formulations have improved both aromatic and reformate yields. UOP has improved the performance of the conventional platforming process by incorporating a CCR system. The process uses stacked radial-flow reactors and a CCR section to... 

Mono- and bimetallic Rh catalysts were evaluated for the stereoselective reductive amination of alkylphenols to the corresponding alkylcyclohexylaniines. Rhodium catalysts as well as bimetallic catalyst formulations with platinum were found to be the most suitable for this one-step hydrogenation. Both the chemo- and the stereoselectivity of that reaction depend on the amoimt of base added and other parameters such as kind of solvent and/or support. 

Rhodium catalysts as well as bimetallic catalyst formulations with platinum have been found most suitable for the one-step hydrogenation of 4-alky henols to the corresponding cis-4-alkylcyclohexylamines in the presence of ammonia (see Figure 2). 

Although the protonated TMH or TMD complexes as formulated above have so far never been observed directly, and are just postulated intermediates, there exists experimental evidence that the dinitrosyl hydride complexes posses a strong basic site at the atom. For example, we were able to characterize A—ON-ReH(NO)(P Pr3)2 adducts, A representing a Lewis acid like BF [52] or even the cationic metal fragment [Re(NO)2(P Pr3)2] itself [50]. The formation of these adducts not only illustrates the basicity of the nitrosyl group, but also the strong Lewis acidity of the 16e cation. We also found that the bimetallic complex shows a similar reactivity as the free cationic species itself. Further evidence for the proposed heterolytic splitting was obtained when the reaction with H2 or D2 is performed in the presence of an external base (Scheme 5). 

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