Effect of synthesis conditions on the catalytic performance of phosphotungstic acid encapsulated metal-organic framework in the oxidative desulfurization

A series of phosphotungstic acid (HPW) encapsulated metal-organic HPW@MIL-101(Cr) catalysts, with high surface area and high activity in the oxidative desulfurization (ODS), were synthesized by one-step hydrothermal method and characterized by FT-IR, XRD and nitrogen physisorption. The influences of synthesis time, temperature, HPW loading, and acidity/alkalinity on the catalytic performance of HPW@MIL-101(Cr) in ODS were then investigated. The results indicated that the order degree of channels in HPW@MIL-101(Cr) is improved with the increase of synthesis time and temperature. The crystal structure of MIL-101(Cr) cannot be formed at a synthetic temperature below 140℃ and the channel order of HPW@MIL-101(Cr) decreases under an acidic synthetic environment. The catalytic activity of HPW@MIL-101(Cr) displays a trend of first increasing and then decreasing with the increase of HPW loading. The HPW@MIL-101(Cr) catalyst with a HPW loading of 3.5 g, synthesized at 220℃ under neutral environment for 12 h, exhibits the highest activity in ODS. At 50℃, with a catalyst dosage of 0.24 g, an model oil of 20 mL, and an O/S molar ratio of 8, the desulfurization rates over the HPW@MIL-101(Cr) catalyst towards benzothiophene, dibenzothiophene, and 4, 6-dimethyl dibenzothiophene after reaction for 120 min reach 99%, 100% and 99%, respectively; in particular, the desulfurization rate for benzothiophene is 2.4 times higher than that obtained over HPW.