Reactions on model emission control catalysts studied by soft X-ray photoemission

Model automotive exhaust catalysts have been studied by evaporating small a mounts of Rh onto thin films of CeO2. Adjusting the O-2 pressure while the film is grown controls the initial oxidation state of the ceria. The ceria oxidation state may change as the system reacts with gaseous species. Ce4d and valence band photoemission are used to determine the Ce oxidation state . Rh3d spectra are used to study the growth of Rh on the CeOX and the respo nse of the Rh particles to CO adsorption. The co-adsorption of NO and CO we re studied on Rh/CeOX. These molecules interact to form OCN at 400 K. At hi gher temperatures the OCN decomposes and various carbon-nitrogen species wi thout O are formed. These CXNY species are relatively stable. They decompos e above 700 K to produce N-2 by N recombination and CO through a reaction o f C with the CeOX. (C) 2001 Elsevier Science B.V. All rights reserved.