Self-assembly of Dawson-type H6P2W18O62@[Cu6O(TZI)3(H2O)6]4 towards high performance of aerobic oxidation desulfurization of fuel

Since the emission standard of global sulfur is escalated, to development of high-efficiency deep desulfurization techniques become imperative. Herein, to design a high-activity heterogeneous catalyst for aerobic oxidation desulfurization (AODS) of fuel, Dawson-type polyoxometalate (H6P2W18O62 abbreviated as D-P2W18), characterized by its high activity and strong oxidative capacity, was applied to react with CuCl2·2H2O and H3TZI by one-pot hydrothermal method. As a result, blue crystalline H6P2W18O62@[Cu6O(TZI)3(H2O)6]4 (abbreviated as D-P2W18@rht-MOF-1; rht-MOF-1 = [Cu6O(TZI)3(H2O)6]4·nH2O) was afforded. X-ray diffraction analysis indicated that D-P2W18 was successfully encapsulated in the two different cages of rht-MOF-1 which is distinct with the crystal structure of Keggin-type POMs@rht-MOF-1. It represents the first crystal structure of Dawson-type POMs@rht-MOF-1. When D-P2W18@rht-MOF-1 was employed as catalyst for AODS under ambient oxygen pressure with assistance of surfactant dioctadecyl dimethyl ammonium chloride (DODMAC), it demonstrated remarkable catalytic capability and recyclability for both model fuel and commercial diesel. Further, the AODS reaction mechanism, identified as a free radical oxidation-reduction process, was verified by way of radical quenching experiments, EPR and XPS analysis. This approach offers a feasible route for synthesis of new Dawson-type POMs@MOFs of heterogeneous catalysts for highly active AODS of fuel.