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

Abstract 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/TiO 2 ) photocatalyst is presented. The TiO 2 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/TiO 2 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/TiO 2 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.