Synthesis Of Vanadium-based Catalysts Supported On 3D G-C₃N₄ And Study On Catalytic Oxidative Deep Desulfurization In Diesel

For the consideration of environmental protection and sustainable development,in recent years,many countries in the world including China have issued strict diesel standards,which have made clear restrictions on the content of sulfide in diesel oil.Therefore,oxidative desulfurization technology as a new desulfurization technology with mild reaction conditions and high desulfurization efficiency for dibenzothiophene sulfide which is difficult to be removed in hydrodesulfurization has attracted extensive attention of researchers.In this paper,based on the"vanadium-based catalyst supporting on three-dimensional porous carbon nitride",a kind of oxidation desulfurization system with molecular oxygen in the air as oxidant was designed to realize the deep removal of different dibenzothiophene sulfur compounds in model oil,and the reaction path and mechanism were studied and speculated.The main tasks are as follows:（1）V-IL/3D g-C₃N₄ supported catalyst with different loading was prepared by solvothermal method.FT-IR,XRD,XPS,SEM,TEM,N₂ adsorption and desorption experiments were used to investigate the morphology and structure of the catalyst.The combination of lipophilic vanadium-based ionic liquid and three-dimensional porous carbon nitride solves the problems of mass transfer in multiphase oxidation reaction system and the separation and regeneration of active center vanadium-based ionic liquid.It can be found from the activity experiment that when m（catalyst）=0.01g,T=120^oC,V（model diesel）=20 mL,v（air）=100 mL/min,t=6 h,V-IL/3D g-C₃N₄ catalyst with 20%loading can achieve 97.2%desulfurization effect,and the catalyst also has excellent desulfurization performance for other sulfur-resistant compounds.The order for desulfurization efficiency is DBT>4-MDBT>4,6-DMDBT.At the same time,V-IL/3D g-C₃N₄ supported catalyst showed stable circulation performance and anti-interference ability.Through the results of GC-MS,it was proved that the oxidation products of sulfur compounds in model diesel were corresponding sulfones.Combined with the results of ESR and radical scavenging experiments,it was found that O₂^·-radical was the intermediate product of the reaction process.（2）V₂O₅/3D g-C₃N₄ supported catalysts with different loading was prepared by using vanadium based ionic liquid as vanadium source and template.FT-IR,XRD,XPS,SEM,N₂ adsorption and desorption experiments were used to investigate the morphology and structure of the catalyst.The results of characterization confirmed the successful preparation and loading of V₂O₅,and the utilization of ionic liquid template successfully solved the problem of metal oxide agglomeration.The results of the activity experiment showed that the residual sulfur content of DBT in the model diesel could be reduced to 1.2 ppm in 5 hours when 30%V₂O₅/3D g-C₃N₄ supported catalyst was reacted with the conditions of m（catalyst）=0.01 g,T=120^oC,V（model diesel）=20 mL,v（air）=100 mL/min.For 4-MDBT and 4,6-DMDBT,the effect also met the requirements of deep desulfurization.More than 95%of the desulfurization efficiency of V₂O₅/3D g-C₃N₄ supported catalyst can be maintained after 7 times of circulation.The catalytic oxidation selectivity is excellent.The reaction mechanism of V₂O₅/3D g-C₃N₄/O₂ system was speculated by GC-MS and ESR.（3）VEG prepared from ammonium metavanadate and glycol was used as the precursor of vanadium source to prepare VO₂/3D g-C₃N₄ supported catalyst with low-cost vanadium oxide as the active center.FT-IR,XRD,XPS,SEM,N₂ adsorption and desorption experiments were used to investigate the morphology and structure of the catalyst.The preparation method effectively solves the problem that the low valence vanadium oxide needs to be synthesized under the conditions of high temperature and inert gas.At the same time,the carrier three-dimensional porous carbon nitride can expose more active sites by loading VO₂ in situ.Under the reaction conditions of m（catalyst）=0.01 g,T=120^oC,V（model diesel）=20 mL,v（air）=100mL/min,t=5 h,the catalyst can realize the effective activation of molecular oxygen,and the removal rate of model diesel by 30%VO₂/3D g-C₃N₄ supported catalyst can reach 98.6%.For 4-MDBT and 4,6-DMDBT that are more difficult to remove can also achieve the removal effect of 98.9%and 99.4%.In the investigation of the interference experiment and circulation experiment,VO₂/3D g-C₃N₄ supported catalyst has excellent performance.The results of GC-MS and ESR show that the product of oxidation reaction is DBTO₂,and the active species in the reaction process is O₂^·-.