Synthesis, Characterization, and Catalytic Performance of Modified Keggin-type Calix[6]arene-like Polyoxometalates

Graphical The two modified rare heterogeneous Keggin-type crystalline heteropolyacid Calix[6]arene-like catalysts were synthesized by one-pot method with PMo 12 or PW 12 , and these were characterized using single-crystal X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), X-ray diffraction (XRD), and elemental analysis, finally, the catalytic performance and reaction kinetics for the two compounds’ effects were compared during the oxidation process. Two modified Calix[6]arene-like polyoxometalates of the Keggin type with similar structures were synthesized under hydrothermal conditions by H 3 PMo 12 O 40 . H 3 PW 12 O 40 , 4H-1,2,4-triazol-3-amine (3-atrz) and copper ions were used as precursors, respectively, bridging organic ligand and transition metals. The result of single-crystal X-ray diffraction and elemental analysis showed that the structural formulas of the two crystalline compounds were: [2(C 6 H 12 N 12 Cu 3 PW 12 O 40 )] (3-atrz-Cu-PW 12 ), and [2(C 6 H 12 N 12 Cu 3 PMo 12 O 40 )] ⋅ 0.5H 2 O (3-atrz-Cu-PMo 12 ). They were composed of two classic Keggin-type polyoxometalate anions and six [Cu(C 2 H 4 N 4 )] + coordination polymers similar to Calix[6]arene. The catalytic studies represented that the two heterogeneous catalysts catalyzed the oxidation of iodide ions in hydrogen peroxide. The catalytic reaction of 3-atrz-Cu-PW 12 only took 30 min and 15 s to complete the reaction. The rate of iodine generation was 6.86×10 −7 mol L −1 s −1 . The 3-atrz-Cu-PMo 12 catalytic reaction needed only 1 min and 51 s, in which the rate of iodine generation was 1.126×10 −5 mol L −1 s −1 . The catalytic reaction rate of 3-atrz-Cu-PMo 12 was 16.35 times higher than 3-atrz-Cu-PW 12 . Both catalysts were reused nine times, and the conversion rate was still 99.96 %, showing excellent catalytic activity and repeatability.