Controlled Synthesis Of Vanadium-niobium Bimetallic Oxides And Their Catalytic Activity In Deep Desulfurization Of Fuel

Currently,a significant amount of global energy demand comes from fossil fuels,and crude oil being one of the main sources.Meanwhile,the steady growth of global automobile numbers,as well as aviation and maritime scales,will continue to put pressure on global crude oil supplies.Typically,such fuels contain large amounts of sulfur compounds that can damage facilities during production,processing,and transportation.After burning,the sulfur compounds can be oxidized and release SO_x,leading to acid rain and endangering human health.Therefore,relevant departments have been working to strictly control the sulfur content of petroleum fuels,and the development of low-sulfur and even sulfur-free fuels has become one of the research hotspots to ensure energy security and protect the ecological environment.Oxidative desulfurization is a green and new technology for removing sulfur compounds from fuel,which has the advantages of being environmentally friendly,energy-saving,etc.Currently,the classification of oxidative desulfurization technology is mainly based on the differences in catalysts,oxidants,and catalytic reaction conditions during the oxidative desulfurization process.In the selection of catalysts,bimetallic oxides have attracted more and more attention due to their ease of recovery and separation,excellent cyclic performance,and high selectivity.In this paper,various catalytic materials with vanadium-niobium bimetallic oxides（VNbO_x）as the active center were synthesized using different methods,such as regulating the crystal phase to produce oxygen vacancies,forming composite catalysts with mesoporous Ti-Si molecular sieves,and adjusting the material morphology,to achieve high efficiency oxidative desulfurization.The main research contents are as follows:（1）The relationship between the formation energy of oxygen vacancies and the different crystal phases（orthorhombic phase O-VNbO_x,tetragonal phase T-VNbO_x）of V-Nb bimetallic oxides（VNbO_x）was accurately regulated to adjust the oxygen vacancy concentration.The formation energy of oxygen vacancies in different crystal phases was calculated by DFT,and it was found that the formation energy of oxygen vacancies in T-VNbO_x was significantly lower than that in O-VNbO_x.At the same time,the EPR detection results were consistent with the DFT calculation results.A higher concentration of oxygen vacancies is conducive to improve the catalytic oxidative desulfurization performance.Experimental results show that T-VNbO_x has better oxidative desulfurization activity than O-VNbO_x.Dibenzothiophene（DBT）was completely oxidized to dibenzothiophene sulfone（DBTO₂）in 6 h at 120℃,while the polarity increased and was easy to remove.The cyclic experiments proved that the T-VNbO_x material has high activity and stability during oxidative desulfurization process.（2）A novel composite material（VNbO_x/m-TS-1）was prepared by impregnating V-Nb bimetallic oxide into mesoporous titanium-silicate molecular sieve（m-TS-1）.The ultrasound impregnation and calcination methods were used to promote the uniform dispersion of active centers and enhance the stability of the composite catalyst.In addition,the Lewis acid sites on the surface of VNbO_x/m-TS-1 acted as adsorption active sites for dibenzothiophene,enhancing the contact between dibenzothiophene and the active sites,and improving the oxidative desulfurization performance of the catalyst.Furthermore,the mesoporous structure of VNbO_x/m-TS-1 reduced the mass transfer resistance of dibenzothiophene.Experimental results showed that VNbO_x/m-TS-1could activate molecular oxygen under mild conditions and oxidize dibenzothiophene in model oil to more easily removable DBTO₂,achieving ultra-deep desulfurization.In addition,a possible oxidative desulfurization mechanism was proposed through GC-MS analysis,ESR detection,and free radical scavenging experiments.Cycling experiments demonstrated that VNbO_x/m-TS-1 exhibited high activity and stability in oxidative desulfurization.（3）A novel porous bimetallic oxide material was prepared by using the polyethylene oxide-polypropylene oxide-polyethylene oxide（P123）as a soft template to create pores in the V-Nb bimetallic oxide material.Aging and calcination methods were employed to increase the stability of the resulting porous bimetallic oxide catalyst.Moreover,the mesoporous structure in the novel bimetallic oxide material provided more reactive sites and facilitated the contact between dibenzothiophene and the active sites as well as reducing mass transfer resistance.Experimental results showed that porous VNbO_x could activate molecular oxygen under mild conditions and achieve ultra-deep oxidation desulfurization after a 5-hour reaction at 120℃.Furthermore,a possible oxidative desulfurization mechanism was proposed through GC-MS analysis,ESR detection,and free radical scavenging experiments.Cycling experiments demonstrated that porous VNbO_x exhibited high activity and stability in oxidative desulfurization.