Bismuth Atom Tailoring of Indium Oxide Surface Frustrated Lewis Pairs Boosts Heterogeneous CO2 Photocatalytic Hydrogenation

Abstract The surface frustrated Lewis pairs (SFLPs) on defect-laden metal oxides provide catalytic sites to activate H2 and CO2 molecules and enable efficient gas-phase CO2 photocatalysis. Lattice engineering of metal oxides provides a useful strategy to tailor the reactivity of SFLPs. Herein a one-step solvothermal synthesis is developed that enables isomorphic replacement of In3+ ions in UV-absorbing In2O3 by single-site Bi3+ ions to generate a new class of full-spectrum UV-Vis-NIR absorbing BixIn2-xO3 materials. Through compositional tuning, these materials prove to be three orders of magnitude more photoactive for the reverse water gas shift reaction (i.e., CO2 + H2 CO + H2O) than In2O3 itself, while also exhibiting notable photoactivity towards methanol production from carbon dioxide (i.e., CO2 + 3H2 CH3OH + H2O). The defective form of In2O3 containing oxygen vacancy sites can create SFLPs involving In3+ nearby the oxygen vacancy, which function as Lewis acidic sites, while lattice oxide O2- act as Lewis basic sites. In this study, it is discovered that the reactivity of these SFLPs can be further enhanced by single-site Bi3+ ion isomorphic substitution of Lewis acidic site In3+, thereby enhancing the propensity to activate CO2 molecules. In addition, the increased solar absorption efficiency and efficient charge separation and transfer of BixIn2-xO3 also contribute to the improved photocatalytic performance. These traits lead to enhanced binding and activation of CO2, exemplifying the opportunities that exist for atom-scale engineering in heterogeneous CO2 photocatalysis, another step towards the vision of the solar CO2 refinery.