The Interaction between NO and CO on Rh-Loaded CeOx(111)

We have used SXPS and TPD to probe the interactions between CO and NO on ceria-supported Rh model catalysts (Rh/CeOx). On a highly reduced ceria substrate the only desorption products were CO and N2. No NO or CO2 were observed, as have been seen on Rh single-crystal surfaces. The desorption profiles of the CO and N2 were much different than the desorption spectra from CO or NO adsorbed alone, suggesting a strong interaction between the CO and NO. C 1s, N 1s, and O 1s photoemission spectra were recorded to determine the surface intermediates. There is little interaction between the CO and NO below 400 K. Near 400 K the CO reacts with atomic N from dissociated NO to form OCN. The isocyanate dissociates near 600 K, producing desorbed CO and carbon–nitrogen species, CXNY, on the surface. The CXNY decomposes above 700 K to produce CO and N2. The reduced ceria substrate introduces several reaction paths that help promote reactions not ordinarily observed on pure Rh. The reduced ceria removes O from the Rh. This inhibits the formation of CO2 and promotes OCN formation. The reduced ceria also promotes the dissociation of CO. After dissociation, the O is removed by the ceria and the atomic C and N react, forming CXNY.