Abstract

This article focuses on the causes, mechanisms, prevention, modeling, and treatment (experimental and theoretical) of deactivation. The causes of deactivation are basically of three kinds: chemical, mechanical, and thermal. The five intrinsic mechanisms of catalyst decay, (1) poisoning, (2) fouling, (3) thermal degradation, (4) chemical degradation, and (5) mechanical failure, vary in their reversibility and rates of occurrence. Poisoning and thermal degradation are generally slow, irreversible processes while fouling with coke and carbon is generally rapid and reversible by regeneration with O₂ or H₂. Catalyst deactivation is more easily prevented than cured. Poisoning by impurities can be prevented through careful purification of reactants. Carbon deposition and coking can be prevented by minimizing the formation of carbon or coke precursors through gasification, by careful design of catalysts and process conditions and by controlling reaction conditions to minimize effects of carbon and coke formation on activity. Sintering is best avoided by minimizing and controlling the temperature of reaction. Regeneration of deactivated catalysts is possible for many catalytic processes and is widely practiced.

The purpose of this article is to provide the reader with a comprehensive overview of the scientific and practical aspects of catalyst deactivation, including mechanisms of catalyst decay, prevention of deactivation, regeneration of catalysts, methods for study and treatment of catalyst decay, and deactivation kinetics. The greatest emphasis is on deactivation and regeneration of heterogeneous catalysts, although decay mechanisms of homogeneous catalysts and enzymes as well as methods of stabilizing these catalyst types are briefly addressed.