Titania Morphology-Dependent Gold-Titania Interaction, Structure, and Catalytic Performance of Gold/Titania Catalysts

Employing anatase TiO2 nanocrystals with predominantly {001} facets, anatase TiO2 nanocrystals with predominantly {100} facets, and TiO2 P25 with predominantly {101} facets as supports, we have comprehensively studied the morphology effect of TiO2 on the Au-TiO2 interaction, structure, and catalytic performance of Au/TiO2 catalysts in C3H6 epoxidation with H-2 and O-2, C3H6 oxidation with O-2, and H-2 oxidation. A strong morphology-dependent interplay between the Au-TiO2 interaction and the catalyst structure was observed. Only Au nanoparticles were present in the Au/TiO2 catalysts and the Au- species was the largest in Au/TiO2{001} due to the creation of surface O vacancies of TiO2{001} upon Au loading, whereas the fraction of Au+ species was largest in Au/TiO2{100} due to the preserved surface stoichiometry of TiO2{100} upon Au loading. In H-2 oxidation, Au/TiO2{100} with the largest fraction of Au+ species was the most active but least selective toward H2O2, whereas Au/TiO2{001} with the largest fraction of Au- species was the most selective toward H2O2. In C3H6 oxidation with O-2, tiny C3H6 conversions with the formation of partial oxidation products were observed at low temperatures, whereas C3H6 combustion occurred at high temperatures. In C3H6 epoxidation with O-2 and H-2, the ensemble consisting of closely connected Au- and Ti4+ on anatase TiO2{001} and {101} facets with weak adsorption ability was the active structure and the Au/TiO2{001} catalyst containing the largest amount of this ensemble was the most active. These results demonstrated morphological engineering of oxides as an effective strategy to optimize the catalytic performance and understand the fundamentals of catalysis involving oxides.