The dynamics of oxygen exchange with zirconia-supported PdO

Isotopic tracer methods involving O-18 and O-16 were used to investigate the dynamics of O-2 adsorption and desorption from the surface of zirconia-supported PdO and the dynamics of O atom diffusion through the bulk of PdO. The rate coefficient for the recombination of O atoms is found to be 1.4 x 10(13) exp(-144,000/RT) s(-1) and the diffusivity of O atoms through bulk PdO is 1.6 x 10(-10) exp(-89,000/RT) cm(2)/s. In both cases, the activation energies are in units of kJ/mol. While oxygen exchange with pure ZrO2 was not observed under the conditions of the present experiments, such exchange did occur to a limited degree when PdO was supported on ZrO2, the degree of exchange increasing with decreasing PdO particle size. (C) 1999 Academic Press.