Selective Hydrogenation via Cascade Catalysis on Amorphous TiO2
Photocatalysis arises as a green, sustainable alternative method for the synthesis of valuable organic chemicals from biomass. However, the photoinduced holes and/or reactive oxygen species are usually fatal to the selective redox process, which would lead to side reactions especially in the presence of water. Herein, we demonstrate a photocatalytic oxidation/hydrogenation cascade catalytic strategy that could manage the efficient conversion (99%) of 5-hydroxymethylfurfural (HMF) to 2,5-bis(hydroxymethyl)furan (BHMF) with high selectivity (~99%). Reaction 1: under UV irradiation, the protons donated by alcohol via the photooxidation and the photoinduced electrons are stored on the amorphous TiO2. Reaction 2: in the “dark”, the H+/e- coupling transfer contributes to the selective hydrogenation of HMF. This route effectively mediates the negative impact of H2O and active species on the selectivity of product. The oriented adsorption from the aldehyde group of HMF as well as the promoted product desorption brought about the high selectivity of BHMF. The cascade catalytic pathway based on the stored H+/e- provides a reliable approach for biomass functionalization.