Enhanced Surface Charge Localization Over Nitrogen-Doped In2O3 for CO2 Hydrogenation to Methanol with Improved Stability

Indium oxide (In2O3) is active and promising for selective hydrogenation of CO2 to methanol. However, it suffers from over-reduction at elevated temperatures, causing deactivation. Herein, a nitrogen-doped In2O3 (N–In2O3) catalyst was prepared using a plasma-intensified nitrogen-doping technology. It is confirmed that nitrogen doping is effective for the stabilization of In2O3. The doped nitrogen enhances the surface charge localization, which inhibits the over-reduction on the oxide surface and limits the generation of excessive surface oxygen vacancies. The doped nitrogen also serves as the active site, synergistically with surface oxygen vacancy, which leads to an enhanced dissociation of CO2 to adsorbed CO* intermediates. The electron-rich nitrogen causes a strong adsorption of CO on N–In2O3 and inhibits the formation of free CO. A significantly improved methanol selectivity with a higher turnover frequency (TOF) is thus achieved on N–In2O3, compared to the un-doped In2O3. For example, at 21,000 cm3 h–1 gcat–1, 300 °C, and 5 MPa, the TOF of N–In2O3 reaches 37.0 h–1 with methanol selectivity of 75.1%, while the TOF of the un-doped In2O3 is only 16.0 h–1 with methanol selectivity of 62.3%. Different from pristine In2O3, N–In2O3 takes the CO hydrogenation route for CO2 hydrogenation to methanol. This explains the reason why the N–In2O3 catalyst possesses improved selectivity for CO2 hydrogenation to methanol.