The effects of the nature and the structure of platinum group catalysts on their poisining and regeneration

Abstract

The poisining of platinum group catalysts (platinum, rhodium, palladium, ruthenium, osmium and Rh-Os alloys) with mercury, sulphur and lead was investigated. A number of examples were given to show that the capability of being poisoned depends not only on the nature of the catalyst but also on its structure and surface morphology. We established that chemical compounds are formed when platinum, rhodium and palladium catalysts are poisoned, whereas no such interaction takes place when ruthenium and osmium catalysts are poisoned. The role of structure manifests itself in the poisoning of mixed catalysts, i.e. Rh-Os alloys. Differences in the type of interaction and the distribution of the poison over the surface, which are determined by the type of catalyst and its structure, were revealed in the poisoning of platinum and rhodium catalysts with sulphur and lead. Electrochemical methods such as anodic polarization at specific potentials and anodic-cathodic cyclic polarization in 0.1 N H 2SO 4 solutions (with electrolyte replacement) were found to be effective in the regeneration of poisoned catalysts. The choice of the method was determined by the type of catalyst and the type of poison, by the interaction of the poison with the catalyst surface which is dependent on the structure and by the behaviour of the poison during the electrochemical treatment of the catalyst.