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

Highlights: • Adsorption and dehydrogenation mechanisms of methane on Pd (1 0 0) surface were studied using DFT calculations. • The optimized structures and adsorption energies were obtained. The energy barriers and reaction energies were calculated. • The presence of oxygen atom inhibited the dissociation of CH_x except for CH₃ group. - Abstract: Using density functional theory (DFT) together with periodic slab models, the adsorption and dehydrogenation mechanisms of methane on clean and oxygen-covered Pd (1 0 0) 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 (1 0 0) 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 (1 0 0) surfaces. The existence of oxygen atom increases the energy barriers obviously and inhibits the dissociation of CH_x (x = 1, 2 and 4) except for CH₃ group