Kinetic model for polycrystalline Pd/PdO x in oxidation/reduction cycles

Abstract

The complex interactions of Pd and O 2 in catalytic oxidation reactors have been characterized by a detailed mechanism based on elementary reactions at the surface and the bulk–surface interface. The mechanism, which adheres to thermodynamic consistency, captures the bulk and surface hysteresis of Pd oxidation/reduction, as observed in TGA/MS experiments in this and other studies. The model distinguishes between three palladium–oxygen interactions—chemisorbed oxygen on a Pd metal surface, surface palladium oxide, and sub-surface palladium oxide. The use of binary interaction potentials between species provides adequate details such that mean field approaches can be employed to model complex hysteresis patterns for a wide range of O 2 pressures and temperatures. Interaction potentials between the surface and subsurface model the destabilization of surface oxide layers with the depletion of subsurface oxygen. Sensitivity analysis and parameter studies of the mechanism reveal that the interaction potentials between surface and bulk phase species must fall within a narrow range in order to capture the width of the reduction/oxidation hysteresis loops observed in the experiments. The resulting modeling from this study provides a basis for building more extensive models for catalytic oxidation on polycrystalline PdO x .