Relations between Surface Oxygen Vacancies and Activity of Methanol Formation from CO2 Hydrogenation over In2O3 Surfaces

As a promising catalyst for methanol synthesis from CO2 hydrogenation, In2O3 has attracted considerable interest due to its high methanol selectivity. Understanding the structure- activity relationship is of critical importance to guide the design of an optimized In2O3 catalyst. By combining density functional theory calculations with microkinetic modeling, we systematically investigated the methanol synthesis over In2O3 (111) and In2O3 (110). The calculated surface phase diagram suggests that no lattice oxygen exists in the top few layers of In2O3 surfaces under experimental conditions. The theoretical activity volcano indicates that there is a clear relationship between the number of reduced surface In layers and the catalytic activity of In2O3 (111) with an optimum of one to two reduced layers. We further explain why the methanol formation activity of the In2O3 catalyst can be optimized by tuning the number of reduced layers through the effect of adding a ZrO2 support. This work provides an explanation of the low activity of the pure In2O3 catalyst and provides a theoretical insight into how to improve the activity.