Insights into the Surface Electronic Structure and Catalytic Activity of InOx/Au(111) Inverse Catalysts for CO2 Hydrogenation to Methanol

Abstract

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 InO_x/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 InO_x nanostructures. At very low coverages of In (≤0.05 ML), the InO_x 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 InO_x nanostructures under CO₂ hydrogenation conditions. These InO_x/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 InO_x/Au(111) produces methanol via methoxy intermediates. Inverse oxide/metal catalysts containing InO_x 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.