Evolution of multiple spillover hydrogen species on anatase titanium dioxide

Hydrogen spillover is a widespread phenomenon on reducible metal oxide surfaces, with numerous observations confirming its occurrence. However, direct physical characterization of the spillover hydrogen species on an oxide catalyst support remains challenging. Differentiating the binding sites of specific spillover hydrogen species has been elusive. Herein, we vary temperature and reductive conditions, then quench and detect the physicochemical character of three distinct spillover hydrogen species on anatase titanium dioxide (TiO₂-A) by deuterium magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, aided by density functional theory. Fast cooling during the sample preparation is crucial in quenching the spillover deuterium species to enable MAS NMR detection. Energetically favorable spillover deuterium species evolve from deuteron to deuteride states with increasing reduction temperature. Prevailing deuteron species reside on the 2-fold-coordinated O_2c site of the TiO₂-A (101) surface at low reduction temperature. At high reduction temperature, deuterides residing at oxygen vacancies (Ti_6c–D–Ti_5c) are formed.