Relations between Surface Oxygen Vacancies and Activity of Methanol Formation from CO₂Hydrogenation over In₂O₃Surfaces

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.