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JournalISSN: 0926-860X

Applied Catalysis A-general 

About: Applied Catalysis A-general is an academic journal. The journal publishes majorly in the area(s): Catalysis & Heterogeneous catalysis. It has an ISSN identifier of 0926-860X. Over the lifetime, 13628 publication(s) have been published receiving 603023 citation(s).
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Journal ArticleDOI
Calvin H. Bartholomew1Institutions (1)
Abstract: The literature treating mechanisms of catalyst deactivation is reviewed. Intrinsic mechanisms of catalyst deactivation are many; nevertheless, they can be classified into six distinct types: (i) poisoning, (ii) fouling, (iii) thermal degradation, (iv) vapor compound formation accompanied by transport, (v) vapor-solid and/or solid-solid reactions, and (vi) attrition/crushing. As (i), (iv), and (v) are chemical in nature and (ii) and (v) are mechanical, the causes of deactivation are basically three-fold: chemical, mechanical and thermal. Each of these six mechanisms is defined and its features are illustrated by data and examples from the literature. The status of knowledge and needs for further work are also summarized for each type of deactivation mechanism. The development during the past two decades of more sophisticated surface spectroscopies and powerful computer technologies provides opportunities for obtaining substantially better understanding of deactivation mechanisms and building this understanding into comprehensive mathematical models that will enable more effective design and optimization of processes involving deactivating catalysts. © 2001 Elsevier Science B.V. All rights reserved.

2,261 citations

Journal ArticleDOI
Philippe Serp1Institutions (1)
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
Abstract: This review gives a survey on the latest most representative developments and progress concerning ionic liquids, from their fundamental properties to their applications in catalytic processes. It also highlights their emerging use for biomass treatment and transformation.

1,369 citations

Journal ArticleDOI
Abstract: As the oil reserves are depleting the need of an alternative fuel source is becoming increasingly apparent. One prospective method for producing fuels in the future is conversion of biomass into bio-oil and then upgrading the bio-oil over a catalyst, this method is the focus of this review article. Bio-oil production can be facilitated through flash pyrolysis, which has been identified as one of the most feasible routes. The bio-oil has a high oxygen content and therefore low stability over time and a low heating value. Upgrading is desirable to remove the oxygen and in this way make it resemble crude oil. Two general routes for bio-oil upgrading have been considered: hydrodeoxygenation (HDO) and zeolite cracking. HDO is a high pressure operation where hydrogen is used to exclude oxygen from the bio-oil, giving a high grade oil product equivalent to crude oil. Catalysts for the reaction are traditional hydrodesulphurization (HDS) catalysts, such as Co–MoS2/Al2O3, or metal catalysts, as for example Pd/C. However, catalyst lifetimes of much more than 200 h have not been achieved with any current catalyst due to carbon deposition. Zeolite cracking is an alternative path, where zeolites, e.g. HZSM-5, are used as catalysts for the deoxygenation reaction. In these systems hydrogen is not a requirement, so operation is performed at atmospheric pressure. However, extensive carbon deposition results in very short catalyst lifetimes. Furthermore a general restriction in the hydrogen content of the bio-oil results in a low H/C ratio of the oil product as no additional hydrogen is supplied. Overall, oil from zeolite cracking is of a low grade, with heating values approximately 25% lower than that of crude oil. Of the two mentioned routes, HDO appears to have the best potential, as zeolite cracking cannot produce fuels of acceptable grade for the current infrastructure. HDO is evaluated as being a path to fuels in a grade and at a price equivalent to present fossil fuels, but several tasks still have to be addressed within this process. Catalyst development, understanding of the carbon forming mechanisms, understanding of the kinetics, elucidation of sulphur as a source of deactivation, evaluation of the requirement for high pressure, and sustainable sources for hydrogen are all areas which have to be elucidated before commercialisation of the process.

1,330 citations

Journal ArticleDOI
Enrique Iglesia1Institutions (1)
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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