Dehydrogenation metal alloy catalysts

A systematic investigation of dehydrogenation activity over a variety of metal alloy catalysts has been made by Schwab and co-workers (51-53), who have successfully interpreted their results in terms of the bulk metal theory. The test reaction used, namely the dehydrogenation of formic... 

Co, Mo and Pd [7], In addition, the activity of the Pd catalyst for the oxidative dehydrogenation of sodium lactate to pyruvate was improved by the addition of Te [8], Recently, sihca-coated Pt-Co alloys and Pt-Pd alloys covered with silica layers were prepared and used as catalysts for ethylene decomposition to form CNTs [6], The structure of the graphene that forms the walls of the CNTs was different for the two catalysts. This result indicates that the nanoscale carbon structure formed by hydrocarbon decomposition was influenced by the type of metal species in the silica-coated metal alloys. Therefore, further research on the hydrocarbon decomposition of sihca-coated alloys using other metal species is needed because it is possible to develop nanocomposites using the silica-coated metal alloy catalyst and nanoscale carbon structures. 

In support of the conclusion based on silver, series of 0.2, 0.5, 1.0, 2.0, and 5.0 % w/w of platinum, iridium, and Pt-Ir bimetallic catalysts were prepared on alumina by the HTAD process. XRD analysis of these materials showed no reflections for the metals or their oxides. These data suggest that compositions of this type may be generally useful for the preparation of metal supported oxidation catalysts where dispersion and dispersion maintenance is important. That the metal component is accessible for catalysis was demonstrated by the observation that they were all facile dehydrogenation catalysts for methylcyclohexane, without hydrogenolysis. It is speculated that the aerosol technique may permit the direct, general synthesis of bimetallic, alloy catalysts not otherwise possible to synthesize. This is due to the fact that the precursors are ideal solutions and the synthesis time is around 3 seconds in the heated zone. 

In some cases a catalyst consists of minute particles of an active material dispersed over a less active substance called a support. The active material is frequently a pure metal or metal alloy. Such catalysts are called supported catalysts, as distinguished from unsupported catalysts, whose active ingredients are major amounts of other substances called promoters, which increase the activity. Examples of supported catalysts are the automobile-muffler catalysts mentioned above, the platinum-on-alumina catalyst used in petroleum reforming, and the vanadium pentoxide on silica used to oxidize sulfur dioxide in manufacturing sulfuric acid. On the other hand, the platinum gauze for ammonia oxidation, the promoted iron for ammonia synthesis, and the silica-alumina dehydrogenation catalyst used in butadiene manufacture typify unsupported catalysts. 

Compounds 1-4, 7-13, and 16 should be appropriate as monomeric precursors for modified PA-MPs, whereas the derivatives 17, 20, and 23 must be polymerized previously. The polymerization can be carried out either dehydrogenative (compounds 20 and 23) by the use of transition metal complex catalysts or by intermolecular hydrosilylation of Si-H to the -C=C- unit (compound 17) to yield crosslinked polymeric precursors for Si-alloyed PA-MPs. 

Demirci investigated the degree of segregation and shifting of d-band centers by metal alloy combinations to improve the direct liquid fuel cell catalyst activity through electronic promotion of the dehydrogenation pathway [57]. He focused on Pt- and Pd-based catalyst for formic acid electrooxidation and looked at the potential impact of surface adatom adsorption of other 3d, 4d, and 5d transition metals. The criteria he imposed for improved catalytic activity on Pt and Pd... 

However, the intermediate product during the oxidation of methanol makes the catalysis complicated, and the reaction rate for making CO out of methanol solution is slow. Moreover, a second metal such as Ruthenium (Ru) is required, which is explained by the bifunctional mechanism. In other words, activation of water or surface oxides at lower potentials makes the CO absorption bond weaker on the PtRu alloy catalyst. In the meantime, oxidative methanol dehydrogenation occurs on Pt by oxygen-like species on Ru, so that species on Pt-Ru pair sites enables the continuous oxidation of CO to CO. ... 

Gryaznov, V.M., M.M. Ermilova, L.S. Morozova, and N.V. Orekhova, Palladium alloys as hydrogen permeable catalysts in hydrogenation and dehydrogenation reactions, ]. Less-Common Metals, 89,529-535,1983. 

Skeletal (Raney ) catalysts are made by a very simple technique. An alloy of two metals in roughly equal proportions, where one metal is the desired catalytic material, and the other is dissolvable in hydroxide, is first made. This alloy is crashed and leached in concentrated hydroxide solution. The soluble metal selectively dissolves, leaving behind a highly porous spongelike structure of the desired catalytic metal. Catalysts formed by this technique show high activity and selectivity, and have found wide use in industry, particularly for hydrogenation and dehydrogenation reactions. 

Array microreactors and mass spectrometry were used to find the best composition of Pt-Pd-Ir for the dehydrogenation of cyclohexane to benzene.210,211 A catalyst library of 37 binary alloys composed of transition metals, Cu, Zn, and Ti or Si, was screened by IR thermography in the hydrogenation of 1-hexyne, and the oxidation of isooctane and toluene.212... 

Copper-catalysts promoted with i) other group VIA or VIIIA metals and ii) alcaline or alcaline earth elements (IA or IIA) are used for selective hydrogenation of various organic compounds (1). Moreover Cu(Co) Zn-Al catalysts were extensively studied for the synthesis of methanol and of light alcohols (2,3). More recently, due to the development of fine chemical processes, detailed studies of copper catalysts were carried out in order to show, like for noble metals, the effect of supports (SMSI), of promoters and of activation-on metal dispersion or reduction, on alloy formation... For example modified copper catalysts are known for their utilization in the dehydrogenation of esters (4-6), in the hydrolysis of nitriles (7), in the selective hydrogenation of nitriles (8), in the amination of alcohols (9)... 

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