Surface Ru-H Bipyridine Complexes-Grafted TiO Nanohybrids for Efficient Photocatalytic CO Methanation.

A series of novel surface Ru-H bipyridine complexes-grafted TiO nanohybrids were for the first time prepared by a combined procedure of surface organometallic chemistry with post-synthetic ligand exchange for photocatalytic conversion of CO to CH with H as electron and proton donors under visible light irradiation. The selectivity toward CH increased to 93.4% by the ligand exchange of 4,4'-dimethyl-2,2'-bipyridine (4,4'-bpy) with the surface cyclopentadienyl (Cp)-RuH complex and the CO methanation activity was enhanced by 4.4-fold. An impressive rate of 241.2 μL·g·h for CH production was achieved over the optimal photocatalyst. The femtosecond transient IR absorption results demonstrated that the hot electrons were fast injected in 0.9 ps from the photoexcited surface 4,4'-bpy-RuH complex into the conduction band of TiO nanoparticles to form a charge-separated state with an average lifetime of ca. 50.0 ns responsible for the CO methanation. The spectral characterizations indicated clearly that the formation of CO radicals by single electron reduction of CO molecules adsorbed on surface oxygen vacancies of TiO nanoparticles was the most critical step for the methanation. Such radical intermediates were inserted into the explored Ru-H bond to generate Ru-OOCH species and finally CH and HO in the presence of H.