Synthesis Of The Heteropolyacid Immobilized Into NH₂MIL-101 And Their Application In Oxidative Desulfurization

Oxidative desulfurization（ODS） is considered one of the most promising pro-cesses to reduce refractory sulfur-containing comounds for its efficiency and low cost.Supported-heteropolyacid catalysts have been widely used in the oxidative desulfuri-zation.A promising method to immobilize heteropolyacid catalysts is to take advantage of the negative charges of the heteropolyacid ions by immobilization heteropolyacid in the materials that contain amine groups.NH₂-MIL-101（Al）shows a high chemical and thermal stability.Given that the NH₂-MIL-101（Al）displays outstanding basic property and it can be easily protonated because of the presence of amines,NH₂-MIL-101（Al）was chosen as the support to synthesize the composite.First,PTA/NH₂-MIL-101 was successfully synthesized for using PTA and NH₂-MIL-101 by impregnation method and characterized by X-ray diffraction（XRD）,high resolution transmission electron microscopy（HRTEM）,Fourier transform infrared spectroscopy（FT-IR）and X-ray fluorescence（XRF）.The composite was applied as the catalyst in the oxidative desulfurization of dibenzothiophene（DBT）with H₂O₂ as the oxidant in n-octane at atmospheric conditions subsequently.The effects of the temper-ature,H₂O₂/DBT molar ratio（O/S）,catalyst dosages and the amount of phase transfer agent on the desulfurization reaction have been investigated in detail.Kinetic experi-ments were also performed for the reaction at different temperatures.The result showed that oxidative reaction followed pseudo-first-order kinetics,and the apparent activation energy for the desulfurization reaction was 34.1 k J/mol.At optimal reaction conditions,the oxidative desulfurization conversion of DBT reached 100%,and there was no sig-nificant decrease in the catalytic activity after four recycles.The results showed that the material exhibited excellent catalytic performance for oxidative desulfurization of DBT.Second,HPMo@NH₂-MIL-101 has been prepared by the one-pot encapsulation method.The composite was characterized by XRD,N₂ adsorption-desorption experi-ment,FT-IR,X-ray photoelectron spectroscopy（XPS）,inductively coupled plasma op-tical emission spectrometry（ICP-OES）and investigated on its oxidative desulfurization of the model fuel oil.The characterization results showed that the HPMo was highly dispersed within the MOF cavities.In the desulfurization process,the pure HPMo ex-hibited comparatively lower desulfurization efficiency than HPMo@NH₂-MIL-101.Under the optimal conditions,the oxidative desulfurization present a pseudo first-order kinetic process,and the apparent activation energies of DBT is 24.6 k J/mol.At last,probable mechanism for the oxidative desulfurization was proposed as fol-lows:The tungsten and molybdenum polyoxometalates with a Keggin structure con-verted to polyoxoperoxo species named as PO₄[MO（O₂）₂]₄^3-（M=W,Mo）in the pres-ence of hydrogen peroxide.Then DBT were oxidized to the corresponding sulfones by PO₄[MO（O₂）₂]₄^3-.