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

Abstract

Because global sulfur emission has escalated, the development of high-efficiency deep desulfurization techniques has become imperative. Herein, to design a high-activity heterogeneous catalyst for the 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 via a one-pot hydrothermal method. Consequently, 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 two different cages of rht-MOF-1, which is distinct from 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 a catalyst for AODS under ambient oxygen pressure with the 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 the synthesis of new Dawson-type POMs@MOFs of heterogeneous catalysts for highly active AODS of fuel.