Effect of Pt Clusters on Methanol Adsorption and Dissociation over Perfect and Defective Anatase TiO2(101) Surface

Methanol adsorption and dissociation on the perfect and defective anatase TiO2(101) surfaces with and without Pt clusters have been studied using density functional theory periodic calculations. On the clean perfect anatase TiO2(101) surface, the energies of molecularly and dissociatively adsorbed methanol are almost equal. The dissociation via O-H scission with an activation barrier of 0.51 eV is the most favorable route among three possibilities: breaking the O-H, C-O, or C-H bond. In contrast, the activation barrier for C-O bond cleavage is as high as 2.56 eV. In the presence of a Pt cluster on the perfect surface, both molecular adsorption and dissociative adsorption via C-O bond scission were enhanced. At low temperatures, methanol prefers to adsorb molecularly at the interface of Pt/TiO2. As the temperature increases, methanol begins to dissociate. The immediate products after breaking the C-O bond are more stable than those formed from breaking either the O-H or C-H bond. On the clean defective surface, methanol prefers dissociative adsorption at the oxygen vacancy site, with its oxygen atom occupying the vacancy site and proton on the two-coordinated oxygen site. Once the oxygen vacancy site is occupied by a Pt particle, it will not be available for methanol dissociation. Consequently, dissociation of methanol will be forced to take place at less active sites. The results were discussed in the context of catalytic production of hydrogen from methanol over the Pt/TiO2 catalyst.