Dissociation of methanol on hydroxylated TiO₂-B (1 0 0) surface: Insights from first principle DFT calculation

The adsorption of methanol on hydroxylated TiO₂-B (1 0 0) surface with bridging and terminal hydroxyl groups has been studied by first principle calculations. On both clean and hydroxylated surfaces with bridging OH group (OH_br), the O-H bond scission is the most favorable dissociation of methanol and the C-O bond scission is also feasible. This indicates the OH_br has little influence on the adsorption of methanol. The terminal OH group (OH_t) plays a major role in the C-H scission of methanol, which is important for the applications associated with the direct use of hydrogen, such as in situ hydrogenation, and hydrogen generation via the photocatalytic reaction. The dissociative adsorption of methanol via C-H scission, which is an endothermic adsorption on other TiO ₂ surfaces, is identified as exothermic adsorption with adsorption energy in the range of -1.54 eV to -1.91 eV around OH_t on TiO ₂-B (1 0 0) surface. The lowest activation barrier for C-H scission is ∼0.80 eV, which is lower than the release heat of molecular adsorption. Moreover, the hydrogen atoms in methanol are easily transferred to the OH _t and then move to nearby O_2c sites to regenerate the hydroxyl group. This proton migration process could result in extra stable chemi-sorption of methanol with an adsorption energy as low as -2.23 eV, which is above twice that of methanol molecularly adsorbed on the surface. Thus, the proton channel feature of OH_t on the surface is borne out by our calculations.