Insights into the Surface Electronic Structure and Catalytic Activity of InO<sub><i>x</i></sub>/Au(111) Inverse Catalysts for CO<sub>2</sub> Hydrogenation to Methanol
Kasala Prabhakar Reddy, Yi Tian, Pedro J. Ramírez, Arephin Islam, Hojoon Lim, Ning Rui, Yilin Xie, Adrian Hunt, Iradwikanari Waluyo, José A. Rodríguez
Abstract
The direct conversion of carbon dioxide (CO 2 ) into methanol (CH 3 OH) via low-temperature hydrogenation is crucial for recycling anthropogenic CO 2 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 CO 2 hydrogenation, In 2 O 3 catalysts are known for their high CH 3 OH selectivity. Subsequent studies explored depositing metals on In 2 O 3 to enhance CO 2 conversion. Despite extensive research on metal (M) supported In 2 O 3 catalysts, the role of In–M alloys and M/In 2 O 3 interfaces in CO 2 activation and CH 3 OH selectivity remains unclear. In this work, we have examined the behavior of In/Au(111) alloys and InO x /Au(111) inverse systems during CO 2 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 CO 2 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 CO 2 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 CO 2 hydrogenation conditions. These InO x /Au(111) catalysts displayed a high selectivity (∼80%) toward CH 3 OH production and an activity for CO 2 conversion that was at least 10 times larger than that of plain In 2 O 3 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 CO 2 → CH 3 OH conversion in processes associated with the control of environmental pollution and the production of high value chemicals.