A kinetic model for methane emission oxidation over Pd-Pt bimetallic monolith catalysts

In this work, kinetics of methane oxidation was studied over bimetallic Pt/Pd/Al2O3 monolith catalysts using temperature-programmed oxidation (TPO) experiments. Different monometallic and bimetallic catalysts were prepared in monolithic structure. The 1 wt% bimetallic catalyst (0.1 Pt-0.9 Pd) showed the best activity in terms of CH4 oxidation. The experimental data were used to develop a CH4 oxidation kinetic model. Two rate equations were developed for methane oxidation over monometallic Pt and Pd catalysts. The activation energy of methane oxidation over Pt and Pd was 124.8 and 55.312 kJ/mol respectively. The 2 rate equations were used to develop a rate equation for Pt-Pd bimetallic catalysts. A multiplying factor was used to account for the interaction of the 2 active sites and to adjust the monometallic rate equations to the bimetallic catalysts. Depending on the composition of bimetallic catalyst, the multiplying factor was a function of various factors. For 1 wt% 0.9 Pt-0.1 Pd and 1 wt% 0.5 Pt-0.5 Pd, temperature was the only factor, which indicated the applicability of the reaction mechanisms over pure Pt and Pd. However, for 1% 0.1 Pt-0.9 Pd, temperature and partial pressures of O-2 and CH4 were the effective factors, indicating a shift from the reaction mechanisms over monometallic Pt and Pd. The distinguished performance of the 1 wt% 0.1 Pt-0.9 Pd was explained, from the bimetallic kinetic model results, by a significant contribution of Pt to the overall catalytic activity of the bimetallic catalysts by minimizing inhibition and decay of Pd sites and/or by increasing the rate of PdO formation. Increasing the Pt percentage to 50% or more resulted in elimination of the role of Pd.