Catalytic oxidation of hydrogen on platinum: Thermochemical approach

Using the thermochemical approach to interpret the kinetics of heterogeneous reactions and the mechanism of congruent dissociative decomposition of solids developed in the 1980s and (re)analyzing the experimental data available in the literature over the last 90 years, a novel mechanism for the catalytic oxidation of H 2 by PtO 2 is proposed. In place of the conventional Langmuir–Hinshelwood and Eley–Rideal adsorption reaction mechanisms, our model is based on the reactions: PtO 2 (s) + 2H 2 ↔ Pt(g) + 2H 2 O and Pt(g) + O 2 ↔ PtO 2 (g) → PtO 2 (s). The first reaction determines the kinetics of H 2 oxidation and the second determines the kinetics of restoration of the PtO 2 layer. Thermochemical consideration of kinetic features of this model enables (for first time in the history of this reaction) the enthalpy and equilibrium constants for H 2 oxidation on platinum to be calculated. The results are in good agreement with experimental data. In addition, the proposed mechanism explains the origin of the surface-retexturing effect, the impact of autocatalysis, the influence of H 2 O vapor on oxidation rate, and the three-fold variation of the Arrhenius E parameter with temperature. This all convincingly demonstrates the value of the thermochemical approach in interpreting heterogeneous reactions.