Tailoring Surface Frustrated Lewis Pairs of In(2)O(3−) (x)(OH)(y) for Gas‐Phase Heterogeneous Photocatalytic Reduction of CO(2) by Isomorphous Substitution of In(3+) with Bi(3+)

Frustrated Lewis pairs (FLPs) created by sterically hindered Lewis acids and Lewis bases have shown their capacity for capturing and reacting with a variety of small molecules, including H(2) and CO(2), and thereby creating a new strategy for CO(2) reduction. Here, the photocatalytic CO(2) reduction behavior of defect‐laden indium oxide (In(2)O(3−) (x)(OH)(y)) is greatly enhanced through isomorphous substitution of In(3+) with Bi(3+), providing fundamental insights into the catalytically active surface FLPs (i.e., In—OH···In) and the experimentally observed “volcano” relationship between the CO production rate and Bi(3+) substitution level. According to density functional theory calculations at the optimal Bi(3+) substitution level, the 6s(2) electron pair of Bi(3+) hybridizes with the oxygen in the neighboring In—OH Lewis base site, leading to mildly increased Lewis basicity without influencing the Lewis acidity of the nearby In Lewis acid site. Meanwhile, Bi(3+) can act as an extra acid site, serving to maximize the heterolytic splitting of reactant H(2), and results in a more hydridic hydride for more efficient CO(2) reduction. This study demonstrates that isomorphous substitution can effectively optimize the reactivity of surface catalytic active sites in addition to influencing optoelectronic properties, affording a better understanding of the photocatalytic CO(2) reduction mechanism.