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

As a promising catalyst for methanol synthesis from CO 2 hydrogenation, In 2 O 3 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 In 2 O 3 catalyst. By combining density functional theory calculations with microkinetic modeling, we systematically investigated the methanol synthesis over In 2 O 3 (111) and In 2 O 3 (110). The calculated surface phase diagram suggests that no lattice oxygen exists in the top few layers of In 2 O 3 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 In 2 O 3 (111) with an optimum of one to two reduced layers. We further explain why the methanol formation activity of the In 2 O 3 catalyst can be optimized by tuning the number of reduced layers through the effect of adding a ZrO 2 support. This work provides an explanation of the low activity of the pure In 2 O 3 catalyst and provides a theoretical insight into how to improve the activity.