KINETICS OF CEO2 SURFACE-AREA REDUCTION IN A MIXTURE OF HCL, H2O, ANDO2

Surface area reduction of a cerium dioxide powder is studied at 900 K in a HCI, H2O, and O2 atmosphere. The rate of surface area decrease is determined as a function of the surface chloride content and of the p artial pressure of hydrogen chloride. It is shown that particle growth occurs due to the surface diffusion of cerium and hydroxyl ions, whic h results from hydrogen chloride adsorption. Adsorbed chloride ions re act to give gaseous chlorine. The rate-determining step of the process of initial coarsening is hydrogen chloride fixation at the surface of cerium dioxide particles.