Heterogeneous Oxidation of Methane over Palladium Catalysts

Abstract

A BRIEF investigation has been made of the effect of different forms of palladium catalysts on the heterogeneous oxidation of methane. The experiments are based on the idea that, if crystals of metal are formed by thermal decomposition of a metal salt which is deposited within the pore structure of a zeolite, the maximum size to which the metal crystallite can grow is equal to the size of the pore or cavity of the zeolite within which decomposition occurs. Because the dimensions of these cavities and pores are in the range of 0.4–4 nm for most zeolites, it is possible to study catalytic reactions on crystallites of these dimensions without interference from the much larger crystallites present in most supported metal catalysts. These catalysts could be prepared by thermal decomposition of a complex metal salt in which the catalytic metal is in an anionic form so that ion exchange with the zeolite metal ions does not occur. In this study we have compared three catalysts: massive palladium metal (catalyst 1), palladium crystallites within a zeolite structure (catalyst 2) and a zeolite catalyst containing separated metal atoms (catalyst 3) produced in the normal way by ion exchange¹.