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XPS investigation of surface changes during thermal aging of Natural Gas Vehicle catalysts: Influence of Rh addition to Pd

This study investigates thermal aging induced effects on the surface properties of model and commercial automotive catalysts for Natural Gas Vehicles, by means of X‐ray photoelectron spectroscopy and infrared spectroscopy of chemisorbed CO as a probe molecule for noble metals. Post‐combustion catalysts for this application are essentially composed of palladium containing low amounts of rhodium and additives to improve the oxygen storage properties. The aging procedure involved exposing the catalysts to an oxidizing atmosphere containing air and 10 vol.% H2O at 980 °C for 4 h in order to simulate surface changes which may occur under usual three‐way operating conditions. It was found that sintering processes led to a significant loss of Pd concentration on model and commercial catalysts. Regarding Rh, diffusion processes into alumina also take place, which are partially inhibited on model catalysts when Rh interacts with Pd. Greater stabilization of Rh species is suggested on commercial catalysts in the presence of oxygen storage materials. Copyright © 2010 John Wiley & Sons, Ltd.