Controllable Visible-Light-Driven Syngas Evolution by a Ternary Titania Hybrid Sacrificial System with a Photosensitive Metal–Organic Pd^II Cage and Re^I Catalyst

A photosensitive metal–organic cage (MOC), denoted as MOC-Q2, consisting of two Pd2+ metal ions and four tridentate ligands, is synthesized, and then MOC-Q2 is linked with titania to obtain a hybrid material TiO2-MOC-Q2, which exhibits remarkable photocatalytic H2 evolution activities. After loading a molecular Re catalyst, the ReP/TiO2-MOC-Q2 (6.5 wt %) photocatalyst demonstrates a selective performance of CO2 reduction to CO in dry CO2-saturated dimethylformamide (DMF) solution. By adjusting only the water content in the reaction system, the ternary catalyst can produce syngas with controlled ratios of CO/H2 varying from 15:1 to 1:2. CO/H2 gas evolution rates of 638/604 and 499/964 μmol g–1 h–1 are gained with a CO/H2 ratio of 1:1 and 1:2 in 5 h experiments, respectively. And the corresponding TONCO/TONH2 in the 20 h persistence test is calculated to be 875/458. This system presents one of the best activities among the reported syngas production photocatalysts without using noble ruthenium complexes. This work provides a promising way for the development of multifunctional heterogeneous MOC-based photocatalysts.