Catalytic oxidation of CO on platinum Thermochemical approach

Using concepts recently developed in thermal decompositions of solids and reduction of bulk oxides by gases and (re)analysis of experimental literature data, a novel mechanism for the catalytic oxidation of CO by PtO2 is proposed. Instead of the conventional Mars-van Krevelen scheme, the reactions proposed are: PtO2(s) + 2CO aY center dot Pt(g) + 2CO(2) and Pt(g) + O-2 aY center dot PtO2(g) -> PtO2(s). The first reaction determines the kinetics of CO oxidation and the second determines the kinetics of restoration of the PtO2 layer. Thermochemical consideration of the kinetic features of this model, based on Langmuir's quasi-equilibrium equations for evaporation of simple substances, allowed calculation of the reaction enthalpy and the absolute rate of CO oxidation. These results are in good agreement with experimental data. The proposed mechanism explains the origin of the surface-retexturing effect, the limited loss of Pt metal from the catalyst, the mechanism of PtO2 regeneration by oxygen, the strong effect of CO2 in reducing the CO oxidation rate and the three-fold variation of the Arrhenius E parameter with temperature.