DFT insight into the support effect on the adsorption and activation of key species over Co catalysts for CO₂ methanation

Our recent experiments for CO₂ methanation reveal that Co catalysts supported on ZrO₂ and Al₂O₃ exhibit good initial activity, but the Co/ZrO₂ catalyst is catalytically more active and more stable than the Co/Al₂O₃ catalyst. Detailed characterization demonstrated that there are notable differences in the adsorption properties of key species between the ZrO₂- and Al₂O₃-supported catalysts and in the metal-support interactions where Co/ZrO₂ shows enhanced adsorption for key species and better reducibility of the cobalt oxide. In the present work, we performed density functional theory (DFT) calculations to provide theoretical insight into the support effect over Co/ZrO₂ and Co/Al₂O₃ for CO₂ methanation in terms of adsorption and activation of key species. The relative adsorption strengths of CO₂, H₂, CO, and CH₄ species on Co/ZrO₂ and Co/Al₂O₃ calculated by DFT showed qualitative agreement with experimental TPD. Importantly, DFT results uncovered an energetically more favorable H₂ dissociative adsorption, faster H* surface migration, and more facile Co-O bond cleavage on Co/ZrO₂ than on Co/Al₂O₃, thus rationalizing the experimentally observed lower temperature and higher degree of cobalt oxide reduction on the ZrO₂ support.