Operando Attenuated Total Reflectance FTIR Spectroscopy: Studies on the Different Selectivity Observed in Benzyl Alcohol Oxidation
Au, Pd, and AuPd supported on TiO2 were prepared by a sol immobilization route. Operando attenuated total reflectance (ATR) IR spectroscopy and catalytic batch reactor experiments were performed in parallel to elucidate the different catalytic performance of the catalysts in the liquid-phase oxidation of benzyl alcohol. Pd/TiO2 exhibited a higher activity than AuPd/TiO2 and Au/TiO2, but the modification of Pd with Au demonstrated a significant stability enhancement. ATR-IR spectroscopy evidenced that the presence of Au facilitates the desorption of byproducts, which thus reduces the extent of deactivation of the active sites caused by the irreversible adsorption of benzoate species. Although benzaldehyde was the main product in both catalysts, the nature of the byproducts differs. Pd/TiO2 favored the deoxygenation of benzyl alcohol to produce toluene as the main byproduct. Conversely, AuPd/TiO2 promoted the transformation of benzaldehyde to benzoic acid.