Hydrogen‐Free Hydrogenation of a Nitrogen‐Containing Ring of Quinolines in an Alcoholic Suspension of a Titanium(IV) Oxide Photocatalyst Modified with Metal Cocatalysts

Abstract TiO 2 photocatalysts having various metal cocatalysts were prepared and used for photocatalytic hydrogenation of quinoline in 2‐propanol suspensions, in which 2‐propanol acted as the hydrogen source in addition to the solvent. Hydrogenation over cocatalyst‐loaded TiO 2 competed with H 2 evolution by the self‐coupling of active hydrogen species over the cocatalyst, and the use of TiO 2 with a Rh cocatalyst resulted in a large 1,2,3,4‐tetrahydroquinoline (THQn) yield and a much larger H 2 yield. In contrast, the use of TiO 2 with an inexpensive Cu cocatalyst resulted in a relatively large THQn yield with greatly suppressed evolution of H 2 , and the hydrogenation was greatly accelerated at slightly elevated temperatures with the rate being almost the same as that with Rh−TiO 2 at the same temperature. Based on the results of a kinetic study, the catalytic properties of Cu−TiO 2 and Rh−TiO 2 are discussed. Hydrogenation over Cu−TiO 2 under solar light was investigated in addition to the expandability and reusability of Cu−TiO 2 .