Sulfide catalysts carbon role

Recently, rhodium and ruthenium-based carbon-supported sulfide electrocatalysts were synthesized by different established methods and evaluated as ODP cathodic catalysts in a chlorine-saturated hydrochloric acid environment with respect to both economic and industrial considerations [46]. In particular, patented E-TEK methods as well as a non-aqueous method were used to produce binary RhjcSy and Ru Sy in addition, some of the more popular Mo, Co, Rh, and Redoped RuxSy catalysts for acid electrolyte fuel cell ORR applications were also prepared. The roles of both crystallinity and morphology of the electrocatalysts were investigated. Their activity for ORR was compared to state-of-the-art Pt/C and Rh/C systems. The Rh Sy/C, CojcRuyS /C, and Ru Sy/C materials synthesized by the E-TEK methods exhibited appreciable stability and activity for ORR under these conditions. The Ru-based materials showed good depolarizing behavior. Considering that ruthenium is about seven times less expensive than rhodium, these Ru-based electrocatalysts may prove to be a viable low-cost alternative to Rh Sy systems for the ODC HCl electrolysis industry. 

Particularly important here is the role of transition metal sulfides. In 1988 Wachtershauser proposed that pyrite, abundant in hydrothermal vent systems, provided an energy source for the first life. He suggested that pyrite provided the catalyst necessary to drive a number of essential chemical reactions which are important precursors to life. More recent studies have confirmed this view and have shown that the sulfides of Fe, Ni, Co, and Zn can play an important role in the fixation of carbon in a prebiotic world (Cody et al., 2004). Transition metal sulfides also play a role in more advance organic synthesis, and Huber and Wachtershauser (1998) showed how amino acids were converted into their peptides using a (NiFe)S catalyst. 

A well-known example of a complex catalytic reaction that takes place on the surface of carbon is the oxidation of hydrogen sulfide [329,330], When water is present on the carbon surface and the surface has the basic pH required for dissociation of H2S, oxidation of the HS ions by active oxygen occurs either to elemental sulfur or sulfuric acid. The latter is formed when the reaction takes place in very small pores, where only sulfur radicals very susceptible for further oxidation to SO3 are formed. Catalytic oxidation also occurs in the case of methyl mercaptan adsorption [331], where on basic carbon, thiolate ions formed as a result of dissociation are further oxidized to dimethyldisulfide strongly adsorbed in the pore system. In the case of desulfurization, inorganic constituents of carbon such as iron and calcium also play a crucial role. Those elements, present even in small amounts, contribute significantly to the oxidation reactions as catalysts [332,333],... 

In addition to studies focusing exclusively on the catalyst surface, the catalyst support (when employed) can play a major role in enhacing the activity/selectivity via morphologic, electronic, and physico-chemical effects. These factors have been extensively explored in the case of thermochemical heterogeneous reactions where a variety of compounds and structures have been successfully used on an industrial scale as catalyst supports (e.g., oxides, sulfides, meso- and microporous materials (molecular sieves), polymers, carbons [251-256]). In electrocatalysis, on the other hand, the practical choice of support in gas diffusion electrodes has been largely limited thus far to carbon black particles. The high electronic conductivity requirement, combined wifli electrochemical stability and cost effectivness, imposes serious restrictions on the type of materials that could be employed as supports in electrocatalysis. 

Solid state reactions discussed here refer to the reactions which have at least one solid as reactants or products. Both the preparation and reduction of fused iron catalyst are solid state reaction processes, but the role of solid reaction has never been studied thoroughly yet, although there are few reports in literatme and textbooks on the preparation and reduction of fused iron catalyst. There is no doubt that the basic reactions during preparation and reduction of fused iron catalysts belong to orderliness of solid state reactions. The reduction and oxidation of solid oxide, the decomposition of carbonates and hydrates, and the oxidation of sulfides etc belongs to solid state reaction. The solid state reaction follows its imique law, and it must be considered in the analysis and interpretation of preparation and reduction of fused iron catalyst. Therefore, it should be understood on the basic law of solid state chemical reactions. 

Another example of the effective role of carbon inertness is the use of carbon-supported catalysts for petroleum hydroprocessing, since in comparison to conventional alumina supports, carbon is exceedingly inert. Thus, when the conversion of a catalyst precursor to the catalytically active phase involves reduction or sulfidation, this is easier and more complete when carbon is the support. The very complete study of De Beer et al. (1984), with a long series of important contributions, initiated by Duchet et al. (1983) provides a clear example of this advantage of a carbon black support, which can be considered as... 

Abstract This chapter deals with the transition-metal-catalyzed hydrothiolation and hydroselenation of alkynes and allenes and related imsaturated compounds with thiols and selenols. In these reactions, the regio- and/or stereoselectivities of the addition products can be controlled by switching the transition metal catalysts. Metal sulfides and selenides (RE-ML , E = S, Se, M = Ni, Pd, Rh, Zr, Sm, etc.) play an important role as key catalyst species in these hydrothiolation and hydroselenation. The introduction of carbon monoxide into these hydrothiolation and hydroselenation systems leads to novel carbonylation with simultaneous addition of thio and seleno groups to unsaturated bonds. 

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