Excess charge driven dissociative hydrogen adsorption on Ti2O4−

Abstract

The mechanism of dissociative D₂ adsorption on Ti₂O₄⁻, which serves as a model for an oxygen vacancy on a titania surface, is studied using infrared photodissociation spectroscopy in combination with density functional theory calculations and a recently developed single-component artificial force induced reaction method. Ti₂O₄⁻ readily reacts with D₂ under multiple collision conditions in a gas-filled ion trap held at 16 K forming a global minimum-energy structure (DO–Ti–(O)₂–Ti(D)–O)⁻. The highly exergonic reaction proceeds quasi barrier-free via several intermediate species, involving heterolytic D₂-bond cleavage followed by D-atom migration. We show that, compared to neutral Ti₂O₄, the excess negative charge in Ti₂O₄⁻ is responsible for the substantial lowering of the D₂ dissociation barrier, but does not affect the molecular D₂ adsorption energy in the initial physisorption step.