Heterogeneous Catalysis: Catalyst Deactivation and Regeneration

By definition, a catalyst is a substance (gas, liquid or solid) that increases the speed and selectivity of a chemical reaction without being consumed by it. But this is not the case: like all inert or living materials, catalysts undergo mechanical, physical and/or chemical alterations that lead to a more or less rapid decrease in their activity, and frequently, their selectivity. This degradation of catalytic properties, known as deactivation, occurs in both homogeneous and heterogeneous catalysis, but this topic of crucial industrial importance naturally receives more attention in heterogeneous catalysis. The diversity and complexity of the phenomena involved in this vast field of deactivation have led us to restrict ourselves to heterogeneous catalysis, with the examples presented selected from two major classes of catalysts: supported metals and acid zeolites.

This article is divided into three parts. The first, devoted to methods for studying the deactivation of solid catalysts, comprises three complementary sections, the first briefly dealing with the simulation and kinetic modelling of deactivation, the second with the characterization of deactivating species, with the emphasis on heavy by-products formed during organic compound transformations (coke), and the third with specific methods for characterizing deactivated catalysts. The second part describes the various deactivation mechanisms: poisoning, fouling, carbon or coke deposition and chemical, physical or mechanical degradation. Naturally, the third part focuses on the solutions developed industrially to prevent or limit catalyst deactivation, and to regenerate them. Although the examples chosen concern only supported metals and acid zeolites, the methods used and the main conclusions are easily extrapolated to other solid catalysts.