Effect of Chlorine on the Chemisorptive Properties of Rh/CeO2Catalysts Studied by XPS and Temperature Programmed Desorption Techniques

Abstract

The effect of residual chlorine, originating from catalyst preparation methods on the chemisorptive properties of Rh/CeO2catalysts, is studied employing X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) techniques on catalysts prepared using Rh(NO3)3or RhCl3·H2O as the metal precursor. XPS experiments show that, following reduction at 300°C, catalysts prepared from RhCl3·H2O contain a significant amount of chlorine species (∼7 at%) while about 30% of cerium exists in the Ce3+state, probably due to the formation of cerium oxychloride (Ce(III)OCl). Rhodium does not undergo complete reduction following treatment in hydrogen at 300°C; a portion of rhodium is in the Rh+state in Rh/CeO2catalyst prepared by Rh(NO3)3while, in addition, Rh3+species are also present in Rh/CeO2prepared by RhCl3·H2O. TPD experiments conducted following hydrogen or carbon monoxide adsorption on both catalysts in the range 25 to 300°C reveal that residual chlorine present on the ceria surface results in suppression of the capacity of the catalyst toward CO and H2adsorption and in changes in the relative population of the adsorbed species.