Copper valence state regulates selectivity in photocatalytic reduction of biomass derivatives with titanium dioxide

Photocatalysis could pave a way to converting biomass resources to high-valued chemicals and fuels under very mild conditions. However, the most popular and active TiO 2 photocatalyst is still encountered with selectivity-controlling troubles because of the complex reactivity between diverse reactants and radicals. In addition, TiO 2 -based catalysts are rarely explored in photoreduction of biomass derivatives. Here, this work reports heterojunction construction of Cu/TiO 2 , Cu 2 O/TiO 2 and CuO/TiO 2 photocatalysts for reductive transformations of bio-aldehydes to the corresponding α,β-unsaturated alcohols under simulated sunlight. CuO/TiO 2 achieves 100% furfural conversion with 96% furfuryl alcohol selectivity and 502 mg FOL g cat. −1 h −1 productivity, outperforming almost all copper- and titanium-oxide based catalysts in the literature to date. Incorporating copper to TiO 2 enables enhanced chemisorption of the C=O bond in furfural on catalyst surface, and moreover, increasing copper valence state can accelerate separation efficiency of photogenerated charge carriers. As a result, furfuryl alcohol selectivity as well as furfural initial conversion rate is significantly boosted. Photoelectrochemical measurements, in situ EPR and DRIFT-IR techniques, and DFT calculations coherently demonstrate photogenerated electrons and holes to be the critical active species driving the selective photoreduction process. Specifically, holes could promote proton reduction via methanol oxidation to generate highly reactive hydrogen species, while electrons would directly participate in the electron transfer process to selectively reduce furfural. To the best of our knowledge, this work can be the first example of success in controlling product selectivity using heterojunction strategy for photocatalytic reductive transformation of biomass derivatives and in achievement of high productivity for α,β-unsaturated alcohols.