Synthesis of aluminum doped MIL-100(Fe) compounds for the one-pot photocatalytic conversion of cinnamaldehyde and benzyl alcohol to the corresponding alcohol and aldehyde under anaerobic conditions

Abstract

Fully utilizing the photogenerated electrons and holes in a photocatalytic process is a promising way to enhance catalytic efficiency and achieve atomic economy. Here, conjugated photocatalytic redox reactions, i.e. hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) and concomitant oxidation of benzylalcohol (BA) to benzaldehyde under visible light, are achieved via creating bimetal MIL-100(Fe1-xAlx) compounds as photocatalysts. MIL-100(Fe0.63Al0.37) exhibits a high conversion (≈100%) of CAL with a high selectivity (≈100%) of COL, while converts BA into benzaldehyde (BAD) with a high yield (≈100%). MIL-100(Fe0.63Al0.37) offers abundant and strong surface Lewis acid sites (Al3+) to activate CAL and BA molecules. In situ FTIR-DRS result indicates that COL is selectively activated via a sbndCO coordination. In situ EPR result reveals that BA molecule is activated to generate Ph-CH2O¯ and H+. Under visible light, Ph-CH2O¯ is oxidized to Ph-CH2O· by photogenerated hole, while the photogenerated electron is responsible for producing H atom through the reduction of the dissociated H+. Then the second H atom is released from Ph-CH2O·, causing the generation of Ph-CHO. The activated CAL is selectively hydrogenated to COL by two H atoms. This work provides a special horizon to effectively design a hybrid metal MOFs photocatalyst and to improve the full utilization of photogenerated electrons-holes in a photocatalytic process.