Synthesis of Porous Confined Ionic Liquid Phosphotungstate Based on MIL-101 and Its Solvent-Free Catalytic Oxidation of Cyclohexene to Adipic Acid

A series of porous confined ionic liquid phosphotungstate were synthesized by encapsulated of N-(3-sulfopropyl)morpholinium phosphotungstate ([C3SO3Hnhm]3 -PW12O40) into MIL-101. Then the aforementioned porous confined ionic liquid phosphotungstate as heterogeneous catalyst will be used together with H2O2 for the catalytic synthesis of adipic acid from cyclohexene. During the experiment, the effect of weight content of [C3SO3Hnhm]3PW12O40 on the catalytic performance was investigated in detail. And the chemical structure of the catalyst was also characterized by XRD, FT-IR, 1H-NMR, SEM–EDX and N2 adsorption–desorption isotherms. Experimental results revealed that the desired products has been successfully prepared, and the best catalytic performance (81.2% yield of the adipic acid) was obtained under the dose of [C3SO3Hnhm]3PW12O40 was 31wt%, which was almost close to the catalytic activity of original [C3SO3Hnhm]3PW12O40 (85.3% yield of the adipic acid), which was also proved the strategy of packaging ionic liquid phosphotungstate with MIL-101 in this research is feasible. Furthermore, recycled catalytic performance of the catalyst under repeat 6 times was evaluated and the result revealed that the yield in adipic acid was still higher than 80.0%, which also proved that the catalytic active component was stable in the catalyst.