EVIDENCE FOR ENHANCED DISSOCIATION OF CO ON RH CERIA/

The adsorption and reaction of CO on Rh particles supported on oxidize d and partially reduced epitaxial ceria films on yttria-stabilized cub ic zirconia (YSZ) (100), (110), and (111) single crystals was studied using temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). The ceria films on YSZ were highly reducible, reac ting with CO adsorbed on Rh particles to produce CO2 during TPD. After reduction of the ceria, however, the CO TPD results contained two fea tures: a low-temperature state resulting from desorption of molecular CO and a high-temperature state resulting from the recombination of C and O atoms produced by CO dissociation at lower temperature. The frac tion of CO which dissociated on YSZ-supported Rh/ceria increased with the extent of reduction of the ceria surface. TPD studies with isotopi cally labeled CO demonstrated that the O atoms produced by CO dissocia tion undergo exchange with oxygen from the ceria lattice. The CO disso ciation reaction was found to be metal specific and was not observed f or either Pd or Pt supported on reduced ceria/YSZ. (C) 1998 Academic P ress.