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

This review deals with the important industrial reaction of formaldehyde manufacture by methanol oxidation over iron molybdate catalysts. Detailed reference is made to the used catalyst, preparation techniques (coprecipitation, sol‐gel like, mechanical mixing, etc.) including unsupported and supported catalysts, promoters and characterization methods. The controversial active phase assignment (stoichiometric versus Mo rich iron molybdate) is discussed. The proposed reaction mechanisms and kinetic laws for the main and side reactions are examined. The catalyst deactivation processes are reviewed and the role of Mo excess on these processes is underlined. Finally conclusions and perspectives are presented.

Methanol Selective Oxidation to Formaldehyde over Iron-Molybdate Catalysts

Fe2(MoO4)3/MoO3 nano-structured catalysts for the oxidation of methanol to formaldehyde

The adsorption and reaction of methanol with iron molybdate catalysts of widely varying Mo/Fe ratio have been investigated using X-ray diffraction (XRD), Raman, temperature-programmed desorption (TPD), and pulsed flow reactor measurements. From these data, we can conclude that Mo is segregated to the surface of all catalysts, even that with only a 1:50 Mo/Fe ratio in the bulk of the sample. There is a very marked difference between the behavior of pure ferric oxide and catalysts with even a small amount of Mo present. The former produces only CO2 as the product of methanol oxidation with no formaldehyde production, yet with only small amounts of Mo in the preparation the sample is already highly selective for formaldehyde. TPD shows the reason for this. For iron oxide, the methanol adsorbs to form a formate intermediate, resulting in CO2 evolution, whereas after addition of Mo the main intermediate seen is the selective one, that is, the methoxy intermediate, which decomposes to produce formaldehyde in th...

Effect of Varying the Cation Ratio within Iron Molybdate Catalysts for the Selective Oxidation of Methanol

Samples of aged catalyst discharged step by step from industrial tubular reactors have been characterized by surface area, chemical analysis, Mossbauer spectroscopy, XPS, electron microprobe and kinetic measurements. (change-para-here) The data so collected allow to suggest reasonable explanations for the various phenomena occurring during catalyst life in the industrial plants.

Solid State Reactions in Fe-Mo Oxide Catalysts for Methanol Oxidation During Aging in Industrial Plants.

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Solid State Reactions in Fe-Mo Oxide Catalysts for Methanol Oxidation During Aging in Industrial Plants.