Coupling plasmonic noble metal with TiO2 for efficient photocatalytic transfer hydrogenation: M/TiO2 (M = Au and Pt) for chemoselective transformation of cinnamaldehyde to cinnamyl alcohol under visible and 365 nm UV light

M/TiO2 (M = Au and Pt) were prepared by a solvothermal method combined with an in situ photoreduction process and their photocatalytic performance for transfer hydrogenation of cinnamaldehyde (CAL) to form cinnamyl alcohol (COL) in the presence of isopropanol was investigated under visible light and 365 nm UV light. Although the photocatalytic transformation of CAL to COL can be realized over both Au/TiO2 and Pt/TiO2, they show different activity order under visible light and 365 nm UV light, ie, Au/TiO2 show superior activity than Pt/TiO2 under visible light, while an opposite activity order was observed under 365 nm UV light. The hydrogenation to form COL over Pt/TiO2 reached a turnover frequency (TOF) of 197 h(-1) under 365 nm UV light, which is among the highest in all the already reported systems for hydrogenation and transfer hydrogenation of CAL to form COL. The superior performance observed over Pt/TiO2 at 365 nm can be ascribed to a synergistic effect of plasmonic Pt and the direct excitation of TiO2. This study not only provides a green method for the transfer hydrogenation of CAL to form COL, but also highlights the great potential of coupling of plasmonic noble metal nanoparticles with semiconductor photocatalysts for light-induced organic transformations. (C) 2018 Elsevier B.V. All rights reserved.