POM-supported metal carbonyl derivatives (PMCDs) represent a family of tremendous potential catalysts owing to their peculiar physical and chemical properties. Yet low-valence transition metal-substituted Dawson-type PMCD catalysts are uncommon. Hence, we synthesized a tricobalt-substituted PMCDs by conventional aqueous solution method, [Na(H2O)5](NH4)7[P2W15O56Co3(H2O)3(OH)3Re(CO)3]·13H2O (1), and characterized by single crystal X-ray diffraction crystallography, IR, and thermogravimetric analyses (TGA), etc. The obtained compound 1 was employed as a catalyst for the oxidation of diphenylmethane (DPM) to benzophenone, giving 96.8% yield in the presence of tert-butyl hydroperoxide (TBHP) and pyridine. The control experiments indicate that Co metal ion plays an important role in the catalytic reactions. As a side note, the electrospray ionization mass spectrometry (ESI-MS) and UV spectroscopy showed that 1 can retain its integrity in solution, and magnetic measurements indicated that 1 exhibited a weaker ferromagnetic interaction at low temperature.