Active states of rhodium in rhodium exchanged Y zeolite catalysts for hydrogenation of ethylene and acetylene and dimerization of ethylene studied with X-ray photoelectron spectroscopy

Abstract

Rh-Y zeolite catalysts were investigated with X-ray photoelectron spectroscopy (XPS) techniques. It was found, for the first time, that Rh (I) was formed in Rh-Y zeolites as a significantly stable intermediate during the reduction of Rh(III) to Rh metal by heat treatment in vacuum. It was revealed that Rh(I) in Rh-Y zeolites was active for the hydrogenation and the dimerization of ethylene, whereas Rh metal was active for the hydrogenation of both ethylene and acetylene. Strong correlations were established between homogeneous Rh complex catalysts and Rh-Y catalysts both in the active oxidation states of Rh and the effect of additives on the reactions. Furthermore, XPS was successfully applied to define not only the chemical nature but also the structure of Rh in zeolites. The structure of Rh in Rh-Y zeolite was suggested to correlate strongly with the chemical nature of Rh.