Adsorption and dehydrogenation mechanism of methane on clean and oxygen-covered Pd (1 0 0) surfaces: A DFT study

Abstract

Using density functional theory (DFT) together with periodic slab models, the adsorption and dehydrogenation mechanisms of methane on clean and oxygen-covered Pd (100) surfaces have been studied systematically. Different adsorption geometries were investigated for CH4 and related intermediates (CH3, CH2, CH, C, H, O and OH). It was found that CH4 and CH3 prefer to adsorb on the top site, CH2 and OH are favorable on the bridge site, while CH, C, O and H species adsorb preferentially on the hollow site. In addition, this work identified the stable co-adsorption configurations for the relevant co-adsorption groups. It was concluded that the effect of co-adsorbed oxygen atom tends to weaken the adsorbate–substrate interaction on the Pd (100) surface. Finally, transition states, energy barriers and reaction energies were determined to confirm the mechanism of dehydrogenation of CH4 on clean and oxygen-covered Pd (100) surfaces. The existence of oxygen atom increases the energy barriers obviously and inhibits the dissociation of CHx (x=1, 2 and 4) except for CH3 group.