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

The interaction of water with solid surfaces: Fundamental aspects

Although technological practice should minimize environmental impact, this is not always economically feasible. During the past decade, for example, there has been increasing global concern over th...

CO2 Reforming of CH4

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.

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Heterogeneous Catalyst Deactivation and Regeneration: A Review

Steam Reforming and Graphite Formation on Ni Catalysts

We have measured the kinetics of the methane decomposition reaction on Ni(111), Ni(100), and Ni(110) single crystal surfaces under the high incident flux conditions of 1 Torr methane. We find for these processes apparent activation energies of 12.6, 6.4, and 13.3 kcal mol−1, respectively. Initial methane sticking coefficients at 500 K vary with the Ni surface, but are all ∼10−8 to 10−7. The Ni(110) surface is the most active, followed by Ni(100) and Ni(111). A large (∼ factor of 20) kinetic isotope effect is seen for CH4 vs CD4 on the Ni(100) surface, whereas none is seen on the Ni(110) surface. A comparison is made between measured thermal sticking coefficients and those calculated from the results of recent molecular beam experiments of CH4 on Ni(111) and Ni(100) surfaces. Agreement of our results with the Ni(100) beam results is poor, whereas agreement with the Ni(111) beam results is very good. A comparison is also made between our results and rates of the catalytic steam reforming reaction of methane.

Kinetics of the activated dissociative adsorption of methane on the low index planes of nickel single crystal surfaces

Modification of chemisorption properties by electronegative adatoms: H2 and CO on chlorided, sulfided, and phosphided Ni(100)

The isotopic exchange between CO chemisorbed on Ni(100) and CO(g) has been studied using thermal desorption spectroscopy. Rapid isotopic exchange occurs at low crystal temperatures, and presumably involves low adsorption energy CO states which are present at high CO coverages on the Ni(100). Exchange is accompanied by rapid equilibration of exchanged CO throughout the entire CO layer.

D. Wayne Goodman

Papers

Kinetics of the activated dissociative adsorption of methane on the low index planes of nickel single crystal surfaces

Modification of chemisorption properties by electronegative adatoms: H2 and CO on chlorided, sulfided, and phosphided Ni(100)

Carbon monoxide chemisorption on Ni(100)—direct detection of adsorbate-adsorbate interactions by desorption kinetic measurements

Interaction of hydrogen, carbon monoxide, and formaldehyde with ruthenium

Interaction of hydrogen, carbon monoxide, and methanol with Ni(100)