Reactivity of hydrogen species on oxide surfaces

Hydrogen species on oxides are widely involved in oxides-catalyzed reactions such as H2/hydrocarbon oxidation, hydrogenation/dehydrogenation, water-gas shift, and water-splitting reactions. Thus identifications of hydrogen species on oxide surfaces and their reactivity are important for fundamental understanding of these oxides-catalyzed reactions. In this Feature Article, we briefly review our research progress on the reactivity of various hydrogen species on oxides, including surface hydroxyl species, hydride species and hydrated protons. We have successfully developed effective strategies of using gas-phase atomic H to controllably create oxygen vacancies and prepare various hydrogen species on oxide model catalysts under ultra-high vacuum (UHV) conditions and using well-defined oxide nanocrystals with different surface structures and oxygen vacancy concentrations to study the H2-oxide interaction under ambient or even higher H2 pressures. Reactivity of various hydrogen species on oxide surfaces has been identified, including local oxygen vacancy-controlled reactivity of OH species, oxygen vacancy-stabilized hydride species, homolytic dissociation of H2 at oxygen vacancies of reduced oxide surfaces into hydride species accompanied by surface oxidation, photoexcited holes-stimulated desorption of hydride species, electron-stimulated desorption of hydride and OH species, and photoexcited electrons-stimulated desorption of hydrated protons. Strong influences of oxygen vacancies in oxides on both stability and reactivity of various hydrogen species on oxide surfaces are highlighted.