Oxide formation and reduction over Pt, Pd, and Ir; A driving mechanism for oscillations in the co oxidation reaction

Abstract

A sensitive gravimetric technique has been used to study the kinetics of oxide formation and reduction by CO of Pd and Ir powders between ~ 100 and ~ 600°C. The oxidation and CO reduction data for Pt, reported previously, and for Pd and Ir, reported herein, were analyzed within the context of a surface oxide rate equation which we previously employed to describe the oscillations in the rate of CO 2 production via the CO oxidation reaction over Pt, Pd and Ir catalysts. The CO reduction rates derived from this analysis are comparable to those used to describe the oscillations theoretically, whereas the oxide formation rates extracted from this analysis are about an order of magnitude too small. However, after taking into account the enhancement of the oxidation rate by surface irregularities and surface segregated silicon impurities that are produced by repeated oxidation-reduction cycles, these results appear to be consistent with the postulated oxidation/reduction mechanism for the oscillations.