Amine functionalized surface frustrated Lewis pairs boost CO2 photocatalysis†‡

Abstract

The archetype surface frustrated Lewis pair (SFLP) that facilitates CO₂ photocatalytic hydrogenation to methanol and carbon monoxide, is an InOH⋯In site positioned in the surface of a nanoscale indium oxide hydroxide, denoted In₂O_3−x(OH)_y. Proximal Lewis acid In(III) and Lewis base InOH of this genre serve as surface active sites that enable the photochemical heterolytic H₂ dissociation and reduction of CO₂ to the mentioned products. The conversion rate enabled by light has been found to far exceed that enabled by heat. Efforts to enhance the CO₂ photocatalytic performance of the SFLP have involved modifications of the Lewis acidity and basicity through isomorphic substitution of In(III) with Bi(III) and changes in the population of oxygen vacancies through control of oxide non-stoichiometry. Replacement of the Lewis base hydroxide InOH by the stronger Lewis base amine InNH₂ heretofore remains unexplored. The strategy described herein to explore this opportunity begins with the synthesis of In₂O_3−x(EDA)_y. This new material is proven to contain an InNH₂⋯In SFLP and its CO₂ photocatalytic performance is demonstrated to outperform that of its In₂O_3−x(OH)_y progenitor. Tailored Lewis acidity and basicity surfaces bring CO₂ photocatalysis another step closer to the vision of solar CO₂ refineries.