Lewis Acid Dominant Windmill-Shaped V8 Clusters: A Bifunctional Heterogeneous Catalyst for CO2 Cycloaddition and Oxidation of Sulfides

Carbon dioxide (CO2) and sulfides in gasoline are the main causes of air pollution. Considerable attention has been devoted to solving the problems, and the catalytic reaction seems to be a good choice. Owing to the high density of Lewis acid (LA) active sites and large numbers of open methoxide groups, polyoxovanadates (POVs) are an undisputed option as a heterogeneous catalyst for the CO2 cycloaddition reaction and catalytic oxidation of sulfides. On the basis of the above, a series of V8 clusters, [(C2N2H8)4­(CH3O)8VIV8O12]·CH3OH (V8-1a), [(C2N2H8)4­(CH3O)4VIV4VV4O16]·4CH3OH (V8-1), [(C3N2H10)4­(CH3O)4VIV4VV4O16]·5H2O (V8-2), [(C6N2H14)4­(CH3O)4VIV4VV4O16]·5CH3OH·2H2O (V8-3), have been legitimately designed and triumphantly isolated. In the synthesis process, three different kinds of Lewis bases (LBs), ethanediamine, 1,2-diaminopropane, and 1,2-cyclohexanediamine, were used to modify LA {V8} clusters to form four diverting windmill-shaped configuration. Among them, the vanadium atoms in V8-1a are +4 valence of VIV, while the vanadium atoms in V8-1–3 are mixed valence states of VIV and VV. Magnetic property investigation indicates that the antiferromagnetic coupling interactions between VIV ions all exist in the four compounds. The compound V8-1 also demonstrated high catalytic activity in the cycloaddition of CO2 to several epoxides under relatively mild conditions (70 °C, 0.5 MPa). More importantly, the reaction pressure 0.5 MPa is the lowest among the high nuclear polyoxometallates (POMs). Furthermore, V8-1 also has an excellent catalytic conversion for the oxidation of sulfides. The catalytic tests manifested that V8-1 was a very efficient difunctional heterogeneous catalyst for CO2 cycloaddition reaction and catalytic oxidation of sulfides.