KINETIC AND STRUCTURAL STUDIES OF OXYGEN AVAILABILITY OF THE MIXED OXIDES PR(1-X)M(X)O(Y) (M=CE, ZR)

One composition of Pr-Ce mixed oxide and a range of compositions of Pr -Zr mixed oxide were prepared by coprecipitation methods and character ized by x-ray powder diffraction, thermogravimetric analysis, and x-ra y photoelectron spectroscopy. Based on phases formed, the PrOy-ZrO2 sy stem in an oxygen-containing atmosphere at moderate temperatures (up t o 800-1000 degrees C) is analogous to that of CeO2-ZrO2. Addition of e ither Ce or Zr to pure Pr oxide affects both the total amount of oxyge n that can be reversibly exchanged between oxide and gas phase and the kinetics of the redox processes. Ce dramatically increases the amount (per Pr atom) and lowers the temperature of exchange, Zr slightly dec reases the amount and also lowers the temperature of exchange, and bot h modifiers speed up the rate. These observations are rationalized in terms of bulk and surface structural features of the mixed oxides.