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.

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Mechanisms of catalyst deactivation

Deactivation of heterogeneous catalysts is a ubiquitous problem that causes loss of catalytic rate with time. This review on deactivation and regeneration of heterogeneous catalysts classifies deactivation by type (chemical, thermal, and mechanical) and by mechanism (poisoning, fouling, thermal degradation, vapor formation, vapor-solid and solid-solid reactions, and attrition/crushing). The key features and considerations for each of these deactivation types is reviewed in detail with reference to the latest literature reports in these areas. Two case studies on the deactivation mechanisms of catalysts used for cobalt Fischer-Tropsch and selective catalytic reduction are considered to provide additional depth in the topics of sintering, coking, poisoning, and fouling. Regeneration considerations and options are also briefly discussed for each deactivation mechanism.

/pdf/heterogeneous-catalyst-deactivation-and-regeneration-a-166g7jwbkh.pdf

Heterogeneous Catalyst Deactivation and Regeneration: A Review

Hydrogen production from methane through catalytic partial oxidation reactions

Research has been carried out to understand the mechanisms under which coke formation occurs and to search for solutions to reduce or eliminate coke deposition. Significant efforts have been exerted over the past twenty years in developing coke-inhibiting methods. Coke inhibitors, i.e., chemical additives, or special coating of metal surfaces which suppress coke formation. Coke inhibitors/surface coating work by passivating catalytically active metal sites through chemical bonding interactions, and/or forming a thin layer to physically isolate the metal sites from coke precursors in a process stream, and/or interfering with those radical reactions leading to coke formation by blocking active radical sites on surfaces. This review paper investigates the effect of the most important methods such as new chemical additives, tube material construction, pretreatment of surface on the coke formation of pyrolysis furnaces.

Coke Formation Mechanisms and Coke Inhibiting Methods in Pyrolysis Furnaces

Thermal stressing of a JP-8 fuel was carried out in an isothermal flow reactor using nickel, stainless steel (316 and 304), Silcosteel, and glass-lined stainless steel tubes at 500 °C wall temperature and 34 atm (500 psig) for 5 h at a liquid fuel flow rate of 1 mL/min. Different length segments along the sample tubes were analyzed to observe the deposit distribution throughout the test section. Temperature-programmed oxidation (TPO) analysis and SEM examination of the stressed tubes showed differences in the amount and nature of the solid deposits obtained on the different substrates. The activity of the tube surfaces toward carbon deposition decreases in the order nickel > SS 316 > SS304 > Silcosteel > glass-lined stainless steel. The catalytic activity of the metal surfaces was noted using TPO analysis in conjunction with SEM examination of the deposited tubes.

Analysis of Solid Deposits from Thermal Stressing of a JP-8 Fuel on Different Tube Surfaces in a Flow Reactor

Inhibition of Coke Formation in Ethylene Steam Cracking

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Inhibition of Coke Formation in Ethylene Steam Cracking