Transition Metal Peroxo Complexes Immobilized On UIO-67 As Catalysts For Oxidative Desulfurization

As the announcement and implementation of National standards V of motor oil,ultra-deep desulfurization of diesel has been considered to be an important direction of future work for refineries and scientific research institutions.Efficient desulfurization technology and the development and application of new type catalysts are bound to become a top priority.In recent years,oxidative desulfurization becomes the focus of research with mild reaction conditions,low investment cost and good oxidation efficiency for heterocyclic sulfur compounds.Metal-organic frameworks attract a lot of attention and research in the application of oxidative desulfurization?ODS?recently as a new kind of organic-inorganic hybrid porous materials with high specific surface area,high porosity,tunable structure and qualitatively modified functionality.Two composite materials,UIO-67-MoO?O₂?₂ and UIO-67-WO?O₂?₂,were synthesized in this paper exploiting 2,2'-bipyridine-5,5'-dicarboxylic acid as organic ligand to immobilize transition metal peroxides MoO?O₂?₂ and WO?O₂?₂ on the metal-organic framework UIO-67 by post-and pre-modification respectively and were used as catalysts for ODS process.The catalysts were characterized by X-ray diffraction?XRD?,Fourier infrared transform spectrum?FT-IR?,low temperature N2 sorption,Inductively coupled plasma atomic emission spectroscopy?ICP-AES?analysis etc.On the fixed bed reactor,we investigated the reactivity and stability of catalysts in oxidative desulfurization and the influence of nitrogen compounds on oxidation reaction using cumene hydroperoxide as the oxidant and sulfur-containing compounds such as dibenzothiophene dissolved in toluene/n-heptane as model diesel.Simultaneously,we explored the radical mechanism of oxidation desulfurization reaction by adding the radical scavenger isopropanol and benzoquinone.The oxidative desulfurization performance of three kinds of heterocyclic sulfur-containing compounds BT,DBT,4,6-DMDBT was studied at 20 ? and 40 ? respectively under the catalysis of UIO-67-MoO?O₂?₂.The reaction results showed that the average conversion of BT?DBT and 4,6-DMDBT were 21.6%?78.5% and 14.7% respectively at 20? while at 40?,the average conversion of them were 47.1%?98.9% and 97.4% respectively.So we chose 40?and DBT as the reaction temperature and sulfuric substrate.Compared with the unmodified UIO-67 and supported catalyst MoO₃/SiO₂,the conversion of DBT can remain above 93% within 70 h under the catalysis of UIO-67-MoO?O₂?₂ while the maximum conversion of DBT only reached 8% and 44% under the catalysis of UIO-67 and MoO₃/SiO₂.With the addition of piperidine in the feed liquid,DBT conversion kept 100% in the first 30 hours but dropped rapidly afterwards,this may due to the attack of N in piperidine to the unsaturated coordination sites of UIO-67-MoO?O₂?₂ generated in the reaction process,hindering further contact between the substrate and the oxidant and catalyst.Under the catalysis of UIO-67-WO?O₂?₂,DBT conversion increased slowly at first and then decreased slowly.Hydroxyl radical scavenger isopropanol showed obvious inhibition to catalytic oxidative removal of DBT with the catalysis of UIO-67-MoO?O₂?₂ and UIO-67-WO?O₂?₂,while the DBT conversion remained unchanged in general before and after the addition of superoxide radical scavenger benzoquinone,indicating that hydroxyl radical was involved in the process of oxidation and superoxide radical didn't exist or involve in the reaction.