Coordinately unsaturated O2c–Ti5c–O2c sites promote the reactivity of Pt/TiO2 catalysts in the solvent-free oxidation of n-octanol

Abstract

A series of TiO₂ anatase materials were synthesized with varying proportions of exposed (101) and (001) facets. Pt was subsequently impregnated onto these materials, which were then exposed to either an aerobic or reductive thermal treatment. The final catalysts were assessed for their performance in the aerobic, solvent free oxidation of octanol. Many kinds of characterization methods were employed to gain insight on how the exposed support facets influenced the catalysis. Thermal reduction of the catalysts led to a loss in the support surface structure, but in the contrary, after calcination, the defined facets remained, which was revealed by Raman and XRD. We further provide evidence that the coordinately unsaturated O_2c–Ti_5c–O_2c sites present in the support promoted the dispersion of Pt after calcination in air, leading to the formation of low-coordinated and electron-deficient Pt clusters, based on high resolution- and spherical- aberration corrected transmission electron microscopy and X-ray absorption fine structure analysis. The calcined catalysts were far more active for both the oxidation of octanol and intermediate octanal, thus resulting in a higher selectivity of octanoic acid. Catalyst performance closely correlated with the proportion of low-coordinated Pt species and the specific surface coordination structure of the support in the catalyst. Subsequent in situ Fourier transfer infrared experiments, conducted using alcohol and aldehydic probe molecules, confirmed that substrate adsorption was strongly influenced by the low-coordinated sites of both the Pt cluster and the exposed surface facets on the support.