Modeling of diffusion process in the isotopic oxygen exchange experiments of CexZr(1-x)O2 catalysts

Abstract

The oxygen mobility processes during the temperature programmed oxygen isotopic exchange is considered by proposed kinetic model. The model includes simple and complex heteroexchange reactions and bulk diffusion processes. The diffusion process is introduced considering monolayers in each separate particle of nanopowder taking into account the decrease of monolayer area with depth inside particle. The model is applied to fit experimental curves of CexZr1-xO2 catalysts with different composition in order to calculate reaction rates and diffusion coefficients, and activation energies of those processes. From the best fit the rates of chemical reactions and diffusion coefficients are found for each composition of catalyst. The dependences of activation energies (reaction and diffusion) and diffusion coefficients versus composition are obtained for CexZr1-xO2 catalysts. Obtained dependencies show nonlinear behavior with passes the maximum values at certain percentage of Ce (or Zr) in CexZr1-xO2 oxide.