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

Abstract A series of porous confined ionic liquid phosphotungstate were synthesized by encapsulated of N-(3-sulfopropyl)morpholinium phosphotungstate ([C 3 SO 3 Hnhm] 3 -PW 12 O 40 ) into MIL-101. Then the aforementioned porous confined ionic liquid phosphotungstate as heterogeneous catalyst will be used together with H 2 O 2 for the catalytic synthesis of adipic acid from cyclohexene. During the experiment, the effect of weight content of [C 3 SO 3 Hnhm] 3 PW 12 O 40 on the catalytic performance was investigated in detail. And the chemical structure of the catalyst was also characterized by XRD, FT-IR, 1 H-NMR, SEM–EDX and N 2 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 [C 3 SO 3 Hnhm] 3 PW 12 O 40 was 31wt%, which was almost close to the catalytic activity of original [C 3 SO 3 Hnhm] 3 PW 12 O 40 (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. Graphic Abstract