Effect of chlorine on the chemisorptive properties of Rh/CeO2 catalysts studied by XPS and temperature programmed desorption techniques

The effect of residual chlorine, originating from catalyst preparation methods on the chemisorptive properties of Rh/CeO2 catalysts, is studied employing X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) techniques on catalysts prepared using Rh(NO3)(3) or RhCl3 . H2O as the metal precursor. XPS experiments show that, following reduction at 300 degrees C, catalysts prepared from RhCl3 . H2O contain a significant amount of chlorine species (similar to 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 degrees C; a portion of rhodium is in the Rh+ state in Rh/CeO2 catalyst prepared by Rh(NO3)(3) while, in addition, Rh3+ species are also present in Rh/CeO2 prepared by RhCl3 . H2O. TPD experiments conducted following hydrogen or carbon monoxide adsorption on both catalysts in the range 25 to 300 degrees C reveal that residual chlorine present on the ceria surface results in suppression of the capacity of the catalyst toward CO and H-2 adsorption and in changes in the relative population of the adsorbed species. (C) 1998 Academic Press.