Catalyst Deactivation and Regeneration

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 O 2 or H 2 . 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.

Deactivation of solid catalysts in liquid media: the case of leaching of active sites in biomass conversion reactions

“…Excellent reviews are reported elsewhere. 24,25 Following Bartolomew, there are basically five 50 types of mechanisms of catalyst deactivation in gas-phase that are compiled in Table 1. These five types can be grouped, based on the nature of the mechanism, as physical, thermal and chemical.…”

“…Numerous reviews, proceedings and investigations address the mechanisms of catalyst deactivation when gas reactants are used and the possibilities of regeneration or 65 prevention of the deactivation. 24,25 . However, much less attention 70 has been paid to understand the deactivation processes in liquid media, probably due to the fact that most of the industrial catalytic processes are carried out in gas phase.…”

“…The main phenomenon in liquid medium is the attrition, causing the size reduction and/or the breakup of the catalyst 85 particles. 24 This can be especially problematic when recovering the catalyst. Formation of fine particles too small to be retained or separated can make the reutilization of the catalyst difficult, especially in fluid or slurry beds.…”

Caracterização de catalisadores automotivos novos e usados visando à reciclagem dos metais

“…Os catalisadores podem perder a sua atividade catalítica, como resultado de uma série de produtos químicos indesejáveis presentes originalmente nos combustíveis e por mudanças físicas [12][13][14][15][16][17]. Os tipos de fenôme-nos da inativação podem ser divididos em três categorias: química, térmica e envelhecimento mecânico [14,15].…”

“…Os tipos de fenôme-nos da inativação podem ser divididos em três categorias: química, térmica e envelhecimento mecânico [14,15]. A inativação ocorre ao longo da vida útil do catalisador, devido a uma ou à combinação de vários fenô-menos.…”