Strong Metal–Support Interaction Mechanisms of Rh Supports in the CO–NO Reaction: Rh/Rh2O3 Interconversion in Promoting NO Dissociation and CO2 Generation

In precious metal catalysts, the interaction between the precious metal and oxide support, denoted the strong metal–support interaction (SMSI), is closely related to catalytic activity. However, there are few studies of the effects of the SMSI on catalytic activity and the properties of catalytic active sites. Therefore, the valence band spectra of Rh catalysts on various supports were measured using X-ray photoelectron spectroscopy and a more surface-sensitive experimental technique, extreme ultraviolet-excited photoelectron spectroscopy. There is a good correlation between the catalytic activities of these Rh catalysts in the CO–NO reaction and the energy difference between the peaks of the Rh metal and Rh2O3 components in the valence band spectra. The cause of the difference in the activities of the Rh catalysts on various supports is analyzed based on density functional theory calculations using two models: Rh metal/support and Rh2O3/support. Rh metal and Rh2O3 contribute to the activity of the CO–NO reaction. NO dissociation is promoted on the Rh metal surface, where the SMSI induces enhanced oxygen adsorption. Conversely, CO oxidation is promoted on the Rh2O3 surface, where the oxygen bonding is weakened by the SMSI. This study reveals the critical mechanisms whereby SMSIs contribute to oxygen-mediated reactions on catalyst surfaces.