Catalyst Poisoning

This chapter elaborates on chemical deactivation, involving a chemically induced change in the catalyst's activity. This change may be related to the competitive, reversible adsorption of the poison precursor (inhibition), to the irreversible adsorption, deposition, or reaction of the poison precursor on or with the surface (poisoning), to the poison-induced restructuring of the surface, or to the physical blockage of the support's pore structure (pore plugging). There are three main categories of catalyst poisoning which need to be distinguished: (1) poison adsorption, (2) poison-induced surface reconstruction, and (3) compound formation between the poison and the catalyst. A large class of catalytic reaction networks requires the presence of multiple functions in the catalyst. There are two ways to induce multifunctionality. Metal oxide catalysts, for example, may inherently possess sites of differing chemical nature (acidic, basic). On the other hand, multifunctionality is also often accomplished by impregnating different metals onto the same support (for example, automobile exhaust catalysts containing Pt, Pd, and Rh).