Reduction of iron oxide by hydrogen spillover over Pt/TiO2 and Pt/Al2O3 surfaces

A two-dimensional model is developed to predict the reduction of iron oxide via hydrogen spillover in Pt/TiO2 and Pt/Al2O3 catalytic systems. The reduction over TiO2 is predicted to be independent of the distance between Pt and iron oxide particles, and is explained by the high surface diffusivity of hydrogen on TiO2. In contrast, the characteristic time for diffusion of hydrogen on Al2O3 is similar to the time scales of the experiment and is strongly dependent on the inter-particle distance, which explains the lower and distance-dependent reduction over Al2O3. It is inferred that hydrogen reaches the TiO2/iron-oxide interface in a short time period, and the reduction rate is primarily governed by the reduction kinetics. The kinetics-governed reduction explanation is also valid for Al2O3, however at longer times when hydrogen has reached the Al2O3/iron-oxide interface. For early time periods, the surface diffusion of hydrogen governs its availability at the Al2O3/iron-oxide interface.