Ultralow Palladium-Loading Pd/1D-TiO2 Catalyst toward Highly Efficient Photothermocatalytic Activity for Solvent-Free Aerobic Oxidation of Alcohols

Precious metal-supported catalytic materials have been widely used in the solvent-free aerobic oxidation of alcohols. However, their high cost limits their industrial application because high catalytic performance is usually obtained at high precious metal loading and O2 pressure. In this work, an ultralow Pd-loading 0.03 wt % Pd/1D-TiO2 catalyst with smaller Pd particles (1.68 nm) is prepared and exhibits a turnover frequency (TOF) value as high as 68191.2 h–1 for the benzyl alcohol oxidation, which is much higher than that of previously reported TiO2-supported catalysts under similar reaction conditions. The results also show that the catalytic activity is strongly dependent on the Pd particle size and light radiation, and a smaller Pd particle size can obviously improve the catalytic reaction rate. Compared to thermocatalytic oxidation, photothermocatalytic oxidation can also obviously improve the catalytic activity and change the main product from >90% benzaldehyde to >60% benzoic acid. A smaller Pd size is beneficial for the benzoic acid formation and decreases the difference in activity between thermocatalytic and photothermocatalytic oxidation. This work provides a valuable method in the green photothermal catalytic synthesis of high value-added chemicals over the ultralow loading precious metal-supported catalysts.