Ultrahigh-Selectivity Photocatalytic Upgrading of Bio-Aldehydes/Diols to Monoalcohols Via In Situ Circumventing Coupling Co-Products Over Janus Single-Atom Pd/TiO2

Photocatalytic transfer hydrogenation of biomass-derived aldehydes to alcohols often results in unwanted coupling co-products. Herein, an ultraselective hydrogen transfer system enabled by in situ oxidative C─C bond cleavage over a Janus single-atom palladium on titanium dioxide (0.5Pd/TiO₂) photocatalyst is presented. The TiO₂ carrier promotes hydrogen-donor activation, while Pd single atoms function as both electron and hydrogen transfer centers, enabling photocatalytic conversion of bio-based furfural to furfuryl alcohol in >99% yield using ethanol as solvent/H-donor at 25 °C. The control/in situ experiments and calculations reveal that ethanol on 0.5Pd/TiO₂ preferentially activates a co-formed coupling by-product to undergo C─C bond cleavage followed by proton-coupled electron transfer, exclusively producing furfuryl alcohol. 0.5Pd/TiO₂ with good reusability is applicable to hydrogenative upgrading of various aldehydes/diols into corresponding monoalcohols with 81‒99% yields. This in situ Janus photocatalytic conversion strategy offers a new approach to eliminate side reactions in reductive upgrading of unsaturated organics/biomass with high selectivity.