Catalyst deactivation

Abstract

An overview of deactivation mechanisms, their causes and consequences, as well as of methods and techniques of investigation of deactivation is presented. There are three fundamental reasons for catalyst deactivation, i.e. poisoning, coking or fouling and ageing. Poisoning can be reversible or irreversible, and with geometric or electronic effect. It can also be selective, nonselective and antiselective, depending on catalyst/poison affinity and kinetics. The action of coke is by direct active sites coverage, or by pore plugging, and depends on reaction conditions, pore's type and catalyst acidity. Kinetics of coking is determined by both mechanism of the coking reaction and its diffusion restrictions. Sintering is the main cause for catalyst ageing. It appears in two forms: thermal or chemical, depending on prevailing reaction parameters, i.e., temperature or concentration. To cope with deactivation two approaches are offered: either to avoid it when possible, like in the case of feed purification, or accept it but with an effort to minimize its effects. Accelerated deactivation tests can be a powerful tools for studying catalyst deactivation in a relatively short time. By proper selection of reaction parameters and applying deactivation compensation approach, reaction and deactivation kinetics can be separated. Based on obtained deactivation kinetics parameters, and by applying appropriate modeling and simulation, the life time of a catalyst and its performance in the commercial reactor at any time can be predicted.