Stepwise Photocatalytic Dissociation of Methanol and Water on TiO₂(110)

We have investigated the photocatalysis of partially deuterated methanol (CD₃OH) and H₂O on TiO₂(110) at 400 nm using a newly developed photocatalysis apparatus in combination with theoretical calculations. Photocatalyzed products, CD₂O on Ti_5c sites, and H and D atoms on bridge-bonded oxygen (BBO) sites from CD₃OH have been clearly detected, while no evidence of H₂O photocatalysis was found. The experimental results show that dissociation of CD₃OH on TiO₂(110) occurs in a stepwise manner in which the O–H dissociation proceeds first and is then followed by C–D dissociation. Theoretical calculations indicate that the high reverse barrier to C–D recombination and the facile desorption of CD₂O make photocatalytic methanol dissociation on TiO₂(110) proceed efficiently. Theoretical results also reveal that the reverse reactions, i.e, O–H recombination after H₂O photocatalytic dissociation on TiO₂(110), may occur easily, thus inhibiting efficient photocatalytic water splitting.