Insights into the Surface Electronic Structure and Catalytic Activity of InO_<i>x</i>/Au(111) Inverse Catalysts for CO₂ Hydrogenation to Methanol

The direct conversion of carbon dioxide (CO2) into methanol (CH3OH) via low-temperature hydrogenation is crucial for recycling anthropogenic CO2 emissions and producing fuels or high value chemicals. Nevertheless, it continues to be a great challenge due to the trade-off between selectivity and catalytic activity. For CO2 hydrogenation, In2O3 catalysts are known for their high CH3OH selectivity. Subsequent studies explored depositing metals on In2O3 to enhance CO2 conversion. Despite extensive research on metal (M) supported In2O3 catalysts, the role of In–M alloys and M/In2O3 interfaces in CO2 activation and CH3OH selectivity remains unclear. In this work, we have examined the behavior of In/Au(111) alloys and InOx/Au(111) inverse systems during CO2 hydrogenation using synchrotron-based ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and catalytic tests in a batch reactor. Indium forms alloys with Au(111) after deposition. The In–Au(111) alloys display high reactivity toward CO2 and can dissociate the molecule at room temperature to generate InOx nanostructures. At very low coverages of In (≤0.05 ML), the InOx nanostructures are not stable under CO2 hydrogenation conditions and the active In–Au(111) alloys produces mainly CO and little methanol. An increase in indium coverage to 0.3 ML led to stable InOx nanostructures under CO2 hydrogenation conditions. These InOx/Au(111) catalysts displayed a high selectivity (∼80%) toward CH3OH production and an activity for CO2 conversion that was at least 10 times larger than that of plain In2O3 or Cu(111) and Cu/ZnO(0001̅) benchmark catalysts. The results of AP-XPS show that InOx/Au(111) produces methanol via methoxy intermediates. Inverse oxide/metal catalysts containing InOx open up a possibility for improving CO2 → CH3OH conversion in processes associated with the control of environmental pollution and the production of high value chemicals.