Hierarchical Carbon Nanocage-Enabled Electron Buffering to Indium Oxide for Efficient CO2 Hydrogenation to Methanol.

The hydrogenation of CO2 to methanol over In2O3-based catalysts is highly sensitive to the concentration of surface oxygen vacancies (Ov). While increasing the Ov concentration can enhance the catalytic performance, it also increases the risk of over-reduction during CO2 hydrogenation, leading to a trade-off between activity and stability. Here, we demonstrate that hierarchical carbon nanocages (hCNCs) act as effective "electron buffering agents" for In2O3, mitigating this trade-off and thereby enhancing the methanol yield, with nitrogen doping of hCNCs further amplifying this effect. Detailed investigations reveal that hCNCs donate electrons to Ov-deficient In2O3 to promote Ov formation, while also extracting electrons from Ov-rich In2O3-x, preventing over-reduction to metallic In. As a result, In2O3 supported on hCNCs maintains a consistently high Ov concentration, enhancing both the catalytic activity and stability. This work highlights the promising potential of hCNCs in the hydrogenation of CO2 to methanol and stimulates interest in their exploitation for other redox catalytic processes.