Controllable redox reaction cycle enabled by multifunctional Ru-containing polyoxometalate-based catalysts

Limited studies have been reported due to the difficulty of synthesizing multifunctional catalysts to realize the redox reaction path cycle. Herein, two multifunctional Ru-containing polyoxometalate-based photocatalysts were prepared via a controllable synthesis strategy. In particular, the catalyst Cs2Na4H7[(SbW9O33)(6){Ru(H2O)(5)}(RuCl3)(RuO6)(2){W(H2O)}(6)(WO)(4){WO2(H2O)}(2){WO2(H2O)(2)}(2){WO5(H2O)}]-43H(2)O exhibited superior catalytic performance compared to the Ru-free isomorphic catalyst. The results demonstrated excellent reaction selectivity obtained by fine-tuning solvent polarity and additives during the catalytic oxidation phase and high catalyst robustness in the photocatalytic reduction phase. The introduction of more ruthenium increases the charge separation efficiency, which is responsible for photocatalysis. For the first time, the closed redox conversion cycle was achieved by a single multifunctional catalyst, where aniline was oxidized into nitrobenzene through a series of separable intermediates (azoxybenzene, azobenzene, and nitrosobenzene), and eventually photoreduced back to aniline. This paper also discusses the relationship between catalytic active site composition and catalytic efficacy, and the underlying reaction mechanisms.