Dissociation of methanol on hydroxylated TiO 2-B (1 0 0) surface: Insights from first principle DFT calculation

Abstract

The adsorption of methanol on hydroxylated TiO 2-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.