Mechanistic Insight into the Hydrodeoxygenation of Hydroquinone over Au/ a-TiO₂Catalyst

The mechanism and kinetic features of hydrodeoxygenation of hydroquinone over the oxygen-defective anatase (a-TiO2) supported gold (Au) catalyst were studied by density functional theory calculations. The investigation of reaction pathways and energetics identified that the conversion of hydroquinone over Au10/a-TiO2(001) went through several key reaction intermediates including benzoquinone, 1,4-cyclohexanediol, and cyclohexanol. The dehydrogenation of hydroquinone to benzoquinone intermediate occurred via H-transfer on both the TiO2 surface and Au cluster. Subsequent hydrogenation of the C = C bonds of benzoquinone mainly occurs from H*-Au sites, which has relatively low barriers, indicating the facile formation of ring-saturated species. The "1,4-cyclohexanediol"pathway dominates the overall reaction in hydroquinone conversion with favorable kinetic feature due to low barriers, leading to a large amount of cyclohexane in the product. The presence of oxygen vacancies on the a-TiO2(001) surface is critically important as active sites to facilitate the cleavage of C-O bond of intermediate species. The interface of Au-TiO2 also plays an important role in stabilizing reaction intermediates and promoting the H transfer between Au cluster and the adsorbed species on the TiO2 surface.