Identifying the Role of Photogenerated Holes in Photocatalytic Methanol Dissociation on Rutile TiO2(110)

As an important model reaction, photocatalytic methanol dissociation on rutile TiO2(110) has drawn much attention, but its reaction mechanism remains elusive. Using DFT+U calculations, we investigate the whole dissociation process of methanol into formaldehyde with and without photogenerated holes, aiming to illustrate how the hole is involved in the dissociation. We find that the O–H dissociation of methanol is a heterolytic cleavage process and is likely to be thermally driven; the presence of a hole has no promotion on the barrier and enthalpy change. In contrast, the subsequent C–H bond cleavage follows the homolytic cleavage mode and is likely to be photochemically driven; great enhancement can be made in both kinetics and thermodynamics when holes are introduced. The essential roles of holes in promoting C–H dissociation are identified, and what kinds of catalytic reactions can or cannot be facilitated by holes is discussed. Our findings may considerably broaden the understanding of photocatalytic chemistry.