Surface Engineering of Indium Oxide by Nickel Oxide Clusters for Driving Methanol Production from CO2 Hydrogenation

Abstract

The hydrogenation of CO2 into methanol offers a promising approach to carbon sequestration and a potential approach to storing hydrogen derived from renewable energy. Herein, we report a facile surface engineering strategy by anchoring nickel oxide (NiO) clusters onto the surface of the commercial indium oxide (In2O3) to drive methanol synthesis. The anchored NiO clusters brought about the transfer of electrons from the NiO cluster to the In2O3 surface, which was revealed through a series of characterizations. This electronic interaction led to an increased level of oxidation of the anchored NiO clusters and facilitated the reduction of the In2O3 surface, thereby generating more active sites such as oxygen vacancies (OVs). More importantly, the anchored NiO clusters contributed to the dissociation activation of H2 compared to the OV site of pure In2O3. As a result, the CO2 conversion and methanol space-time yield were increased by approximately 2-fold and 1.4-fold, respectively. The high-pressure operando Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) measurements suggested that the methanol production was promoted by the formation of formate (HCOO*) and its subsequent conversion to methoxy species (CH3O*). The in situ X-ray adsorption experiments under working conditions indicated that the anchored NiO clusters remained in the oxidized state, with a slight partial reduction. This likely guaranteed the activation of H2, which not only contributed to the formation of more surface-active OVs during the reaction but also offered more active H species in the stepwise hydrogenation reactions for methanol synthesis.