Diffuse reflectance FT-IR study of the deactivation and reactivation of potassium carbonate-supported sodium catalysts for propene dimerisation

Abstract

Diffuse reflectance FT-IR has been used to investigate the chemical processes involved in the deactivation of Na/K 2CO 3 propene dimerisation catalysts and their reactivation by treatment with hydrogen (hydriding). The data show that deactivation of the catalyst is due to the buildup of an involatile unsaturated hydrocarbon material on the surface of the Na/K 2CO 3 catalyst. The deactivating hydrocarbon material is removed from the deactivated catalyst by hydriding at elevated temperatures, the rate of removal increasing with temperature. Hydriding initially produces propene, some of which subsequently undergoes hydrogenation to propane. Deuteriding produces a partially deuterated propene, which is converted to a partially deuterated propane with time. The origin of the deactivating hydrocarbon material is probably by polymerisation of the equilibrium mixture of methyl acetylene and allene, which are formed by secondary processes during the dimerisation of propene. Breakdown of the polymer backbone appears to be the process by which propene is formed during hydriding.