Theoretical Investigation of Methane Oxidation on Pd(111) and Other Metallic Surfaces

Density functional theory and microkinetic modeling are employed to investigate CH 4 oxidation to CO, CO 2, CH 2 O, and CH 3 OH on Pd(111) under mildly oxidizing conditions. Although our energetic analysis indicates that the metallic site on Pd(111) is more active than O* and OH* on the Pd surface for C–H bond activation, our microkinetic analysis indicates that the metallic site produces mostly CO, whereas the O* site produces mostly CH 2 O. In addition, we show that the product selectivity can change significantly depending on the pressures of the products (CO, CO 2, CH 2 O, and CH 3 OH). Increasing the product pressures leads to the promotion of CO 2 production, because CO oxidation becomes more active than CH 4 oxidation. We then extend the study to other FCC(111) surfaces by incorporating the linear scaling relations in the mean-field microkinetic model. We find that most transition-metal surfaces cannot effectively activate CH 4 under the reaction conditions employed. We find that the kinetics of CH 4 oxidation to CO, CO 2, CH 2 O, and CH 3 OH can be described generally as a function of two descriptors, enabling identification of the most promising catalyst surface for selective production of the desired product.