Single Ti³⁺Ion Catalyzes NO Reduction on Stoichiometric Titanium Oxide Cluster Anions (TiO₂)_n^-(n = 1-11)

Titanium dioxide (TiO2) is an important oxide material owing to its extraordinary catalytic reactivity in a wide range of applications. Different species on the surface of TiO2 have been proposed to contribute to its reactivity, while the intriguing catalytic role of a Ti3+ ion has not been substantiated to date. Herein, benefiting from state-of-the-art mass spectrometry and quantum chemical calculations, we demonstrated that an exposed single Ti3+ ion on stoichiometric titanium oxide clusters (TiO2)n- (n = 1-11) works independently to catalyze NO reduction by CO. The single-electron mechanism to reduce NO into N2O was discovered, and an atomic oxygen radical (O•-) on products (TiO2)nO- that is highly reactive (e.g., in CO oxidation) was created. This finding is pivotal for providing a fundamental strategy to utilize an isolated Ti3+ ion on the surface of TiO2 and points out that this catalytic behavior can be a potential pathway in the atmosphere for pollutant removal.