Surface Reconstruction-Induced Photocatalytic Methanol Reduction Reaction on a Rutile TiO₂(001) Surface

Photochemistry of methanol on TiO₂ surfaces is of great importance both fundamentally and industrially. Methanol was previously reported only to occur photogenerated hole-participating oxidation reactions on TiO₂ surfaces. Herein, we report that, upon UV light illumination, the methoxy species formed by methanol dissociation at the 5-fold coordinated Ti⁴⁺ sites (CH₃O(a)_Ti5c) of a reconstructed rutile TiO₂(001)-(1 × 1) surface also undergoes the C-O bond cleavage into methyl fragments mediated by photogenerated electrons, in addition to the well-established photogenerated hole-participating oxidation reactions. Upon subsequent heating, the resulting methyl species undergoes hydrogenation and coupling reactions into methane and ethane, respectively. Accompanying theoretical calculations showed that the lowest unoccupied molecular orbital (LUMO) of CH₃O(a)_Ti5c is localized almost at the conduction band minimum of the CH₃O-adsorbed reconstructed rutile TiO₂(001)-(1 × 1) surface, indicating the likely TiO₂ → CH₃O(a)_Ti5c interfacial photoexcited-electron transfer. These results greatly broaden the photochemistry of methanol on TiO₂ surfaces and demonstrate a photocatalytic methanol-to-hydrocarbon reaction route.