A Purely Inorganic Quasi-Keggin Polyoxometalate for Photocatalytic Conversion of Carbon Dioxide to Carbon Monoxide.

A pure inorganic cluster, H47 Na2 Co4 Mo24 (PO4 )11 O72  ⋅ 15H2 O (denoted as {Co4 Mo24 }), has been successfully synthesized by hydrothermal method. Notably, the assembly of a central {Co2 PO4 } tetrahedron and four peripheral {Co[P4 Mo6 ]} fragments gives rise to a rare "quasi-Keggin" structure of {Co4 Mo24 }, in which Co linkers continue to bridge adjacent substructures, resulting in the generation of 3D framework with large cavities. Benefitting from the combination of strong reductive {P4 Mo6 } units and Co active centers, the photocatalytic system with {Co4 Mo24 } as heterogeneous catalyst exhibits excellent activity for CO2 conversion to CO, offering the CO formation rate of 1848.3 μmol g-1 h-1 with high selectivity of 97.0 %. Besides, thermogravimetric and X-ray diffraction analysis confirm that {Co4 Mo24 } can maintain stable during the photocatalytic reaction process.