Poisoning and deactivation of palladium catalysts

Some of the major causes for deactivation and premature degradation of palladium catalysts are briefly summarised. These include particle growth for various reasons, coke deposition and coke transformation, the influence of the support material on long term stability and modifications at the palladium surface itself such as valency changes or the formation of simple but stable molecular surface species. In addition, variations of physical properties as well as chemical poisoning, corrosion and leaching are discussed. In spite of the large body of literature concerning the common phenomenon catalyst deactivation specific information accessible for the various kinds of palladium catalysts being used worldwide is still quite limited. There is a serious need for future studies on properties of palladium-based catalytic systems regarding, for example, the interactions between carbon, hydrogen and supported palladium as a ternary system. Observations on different deactivation processes on Pd/SiO2 catalysts occuring under industrial conditions are compiled. It was tried to roughly differentiate between different degrees of coking and coke transformation in mainly thermally or purely catalytically driven catalyst coking on the one hand and of moderate or enhanced corrosion phenomena or changes of the properties of the palladium itself on the other. (C) 2001 Elsevier Science B.V. All rights reserved.