Preparation Of Niobium-based Catalyst And Deep Desulfurization Of Oxidized Diesel Fuel

With the development of society,people’s demand for diesel gradually increases.The composition of diesel is relatively complex,and the sulfides contained in diesel will produce a large amount of SO_xafter combustion.When SO_xreleases into the air,it not only causes environmental pollution,but also endangers human health.Therefore,countries around the world have established strict standards for the sulfur content in diesel,and developing appropriate methods to reduce the sulfur content in diesel has become an important research topic.Oxidative desulfurization（ODS）technology has attracted widespread attention due to its high selectivity and efficient removal of difficult to remove aromatic sulfides in diesel fuel.In this paper,Niobium pentoxide（Nb₂O₅）,a transition metal oxide,is used as the active center to design and synthesize a series of niobium-based catalysts.Oxygen is selected as the oxidant to construct a catalytic oxidative desulfurization system.The removal effect on sulfide such as dibenzothiophene and the desulfurization mechanism are investigated.The main research contents are as follows:（1）A series of Nb₂O₅catalysts with different crystal forms were synthesized by adjusting the calcination temperature.It was found that with the increase of calcination temperature,the crystal form and morphology of Nb₂O₅changed.Subsequently,the oxidative desulfurization performance of the synthesized Nb₂O₅catalysts were investigated,and the experimental results showed that the 650-Nb₂O₅catalyst synthesized by calcination at 650℃for 5 hours had the best oxidative desulfurization efficiency.Under the condition of m（Nb₂O₅）=0.05 g and T=130℃,the oxidative desulfurization with 650-Nb₂O₅catalyst reached 100%on the model oil containing DBT after 7 hours of reaction.The removal effect of catalysts on different sulfur-containing substrates is as follows:DBT>4-MDBT>4,6-DMDBT.After 8cycles,the catalytic activity of DBT can still be maintained above 95%.Through free radical scavenging experiments and ESR characterization,it was found that superoxide radicals（·O₂^-）were generated during the oxidative desulfurization process;Through GC-MS characterization,it was found that dibenzothiophene was finally oxidized to the corresponding sulfone.Based on the above experiments and characterization results,the mechanism of catalytic oxidation desulfurization was proposed.（2）G-C₃N₄was synthesized as a carrier through simple calcination,and the active center Nb₂O₅was loaded onto the carrier through solvothermal method.The synthesized carrier g-C₃N₄and the loaded catalyst were characterized by UV-Vis DRS and X-ray photoelectron spectroscopy（XPS）.The results showed the successful synthesis of the carrier g-C₃N₄and the successful loading of the active center.The oxidative desulfurization performance of Nb₂O₅/g-C₃N₄catalysts with different loading amounts was investigated.It was found that the 40%Nb₂O₅/g-C₃N₄catalyst had the best oxidative desulfurization effect under the conditions of m（catalyst）=0.05g,V（oil）=20 m L,v（air）=120 m L/min,T=130℃,and t=5 h.The desulfurization rate of the model oil can reach 100%,and it has a good removal effect on different sulfur-containing substrates,achieving the goal of deep desulfurization.In the interference resistance test of the catalyst,it was found that 40%Nb₂O₅/g-C₃N₄catalyst would not be interfered by olefins（cyclohexene）,but polycyclic aromatic hydrocarbons（naphthalene）would affect the desulfurization efficiency.In addition,the cycling performance of the catalyst was also investigated,and it was found that the desulfurization rate decreased after the fifth cycle,but the removal rate of DBT remained above 95%,indicating that the catalyst has good cycling performance.The oxidative desulfurization mechanism of 40%Nb₂O₅/g-C₃N₄catalyst was investigated through free radical scavenging experiments,ESR characterization,and GC-MS test.（3）The support ZSM-5 was synthesized by seed crystallization method,and the active center Nb₂O₅was loaded onto the support using solvothermal method to prepare Nb₂O₅/ZSM-5 catalysts with different loading amounts.The catalytic oxidative desulfurization performance of catalysts with different loading amounts was investigated,and it was found that 20%was the optimal loading amount.Subsequently,the catalytic performance of the 20%Nb₂O₅/ZSM-5 catalyst for different sulfur containing substrates and interfering substances was investigated under conditions of m（catalyst）=0.05 g,V（oil）=20 m L,v（O₂）=120 m L/min,T=130℃,t=7 h,and it was found that the catalyst has good stability.In the cyclic experiment,it was found that the desulfurization rate of the supported catalyst only slightly decreased after 7 cycles.Finally,through free radical scavenging experiments and GS-MS testing,it was confirmed that the active group·O₂^-free radical was generated during the reaction process,and DBT was oxidized into the corresponding sulfone DBTO₂.