Rh4 cluster supported on the In2O3(111) surface for enhancing the turnover frequency of CO2 hydrogenation to methanol: The application of energetic span model

The turnover frequency of CO2 hydrogenation to methanol on the surface of Rh4 cluster supported In2O3(1 1 1) is investigated using the first-principles calculation. The Rh4 cluster and H2 promote oxygen vacancy formation, which facilitates the interaction between the Rh4 cluster and the In2O3(1 1 1) carrier and improves the stability of catalyst. The adsorption behavior of CO2 and H2 on catalyst is predicted by electrostatic potential and Fukui(−) index. The loading of Rh4 cluster promotes the adsorption of CO2 and allows easier dissociation of H2 compared to the In2O3(1 1 1)_D surface. Afterwards, Gibbs free energy diagrams of three hydrogenation pathways are established and the turnover frequencies of all possible routes are calculated based on the energetic span model. The results reveal that the HCOO pathway is regarded as the optimum hydrogenation mechanism due to its greatest turnover frequency (3.02 × 10−5 s−1), higher than that of In2O3(1 1 1)_D and other reported catalysts. The specific process is CO2(g) + 6H → HCOO* + 5H → HCOOH* + 4H → H2COOH* + 3H → H2CO* + 2H + H2O(g) → H2COH* + H + H2O(g) → CH3OH(g) + H2O(g), while the RWGS pathway and by-products are effectively inhibited, thus enhancing the selectivity of methanol. The improvement in catalytic activity may result from the loaded Rh4 cluster facilitating the adsorption of CO2 and the dissociation of H2.