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Catalyst support

About: Catalyst support is a(n) research topic. Over the lifetime, 18605 publication(s) have been published within this topic receiving 497486 citation(s).

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TL;DR: The ability of different metal surfaces and of the enzymes nitrogenase and hydrogenase to catalyze the hydrogen evolution reaction is analyzed and a necessary criterion for high catalytic activity is found: that the binding free energy of atomic hydrogen to the catalyst is close to zero.
Abstract: The electrochemical hydrogen evolution reaction is catalyzed most effectively by the Pt group metals. As H2 is considered as a future energy carrier, the need for these catalysts will increase and alternatives to the scarce and expensive Pt group catalysts will be needed. We analyze the ability of different metal surfaces and of the enzymes nitrogenase and hydrogenase to catalyze the hydrogen evolution reaction and find a necessary criterion for high catalytic activity. The necessary criterion is that the binding free energy of atomic hydrogen to the catalyst is close to zero. The criterion enables us to search for new catalysts, and inspired by the nitrogenase active site, we find that MoS2 nanoparticles supported on graphite are a promising catalyst. They catalyze electrochemical hydrogen evolution at a moderate overpotential of 0.1−0.2 V.

2,776 citations

Journal ArticleDOI
Abstract: This review analyses the literature from the early 1990s until the beginning of 2003 and covers the use of carbon nanotubes (CNT) and nanofibers as catalysts and catalysts supports. The article is composed of three sections, the first one explains why these materials can be suitable for these applications, the second describes the different preparation methods for supporting metallic catalysts on these supports, and the last one details the catalytic results obtained with nanotubes or nanofibers based catalysts. When possible, the results were compared to those obtained on classical carbonaceous supports and explanations are proposed to clarify the different behaviors observed.

1,664 citations

Journal ArticleDOI
01 Jan 1998-Carbon
Abstract: The increasing importance of carbon materials in catalytic processes is analyzed in terms of the most important characteristics of these materials when acting as catalysts or catalyst supports. Thus, surface area, porosity, chemical inertness and oxygen surface groups affect not only the preparation, but also influence the resistance to sintering and the catalytic activity and selectivity of the catalyst. Several series of catalysts, mainly carbon-supported catalysts, are used to show the possible advantages of carbon as support and the series of variables to be taken into account when selecting a carbon as catalyst support for a given reaction. The role of carbon properties when acting as a catalyst in its own right is also analyzed.

1,504 citations

Journal ArticleDOI
Abstract: Metal particles grown by vapour deposition on clean and well-defined oxide surfaces are used as model catalysts. These new model catalysts allow, unlike metal single crystals, a study of size and support effects in heterogeneous catalysis. The structure, the electronic properties and the reactivity of these supported model catalysts have been studied, in situ, by a large number of surface science techniques. In order to get relevant information from those studies it is necessary to control the nucleation and growth in order to get uniform collections of metal particles. The preparation conditions and the characterisation methods will be reviewed. Particles with well-defined shapes are obtained by epitaxial growth at high temperature on clean ordered surfaces. The electronic properties of the small metal particles depend not only on their size but also on their shape. The chemisorption properties are strongly related to the surface structure of the particles. The interplay between the surface structure, the local electronic properties and the adsorption energy will be discussed for CO chemisorption. The presence of the support plays an important role in the control of the particle morphology. Furthermore, it can increase the adsorption rate. The intrinsic heterogeneity of the supported model catalysts has to be taken into account to understand in detail the catalytic reactions. The reaction rate cannot be considered as an average on the different crystalline facets present on the particle. Finally, we will discuss the possibility to study in situ and at the atomic level simple chemical reactions on supported catalysts.

1,336 citations

Journal ArticleDOI
Abstract: Catalyst productivity and selectivity to C5+ hydrocarbons are critical design criteria in the choice of Fischer-Tropsch synthesis (FTS) catalysts and reactors. Cobalt-based catalysts appear to provide the best compromise between performance and cost for the synthesis of hydrocarbons from CO/H2 mixtures. Optimum catalysts with high cobalt concentration and site density can be prepared by controlled reduction of nitrate precursors introduced via melt or aqueous impregnation methods. FTS turnover rates are independent of Co dispersion and support identity over the accessible dispersion range (0.01–0.12) at typical FTS conditions. At low reactant pressures or conversions, water increases FTS reaction rates and the selectivity to olefins and to C5+ hydrocarbons. These water effects depend on the identity of the support and lead to support effects on turnover rates at low CO conversions. Turnover rates increase when small amounts of Ru (Ru/Co<0.008 at.) are added to Co catalysts. C5+ selectivity increases with increasing Co site density because diffusion-enhanced readsorption of α-olefins reverses, β-hydrogen abstraction steps and inhibits chain termination. Severe diffusional restrictions, however, can also deplete CO within catalyst pellets and decrease chain growth probabilities. Therefore, optimum C5+ selectivities are obtained on catalysts with moderate diffusional restrictions. Diffusional constraints depend on pellet size and porosity and on the density and radial location of Co sites within catalyst pellets. Slurry bubble column reactors and the use of eggshell catalyst pellets in packed-bed reactors introduce design flexibility by decoupling the characteristic diffusion distance in catalyst pellets from pressure drop and other reactor constraints.

1,317 citations

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