Construction Of Defective And Porous Hexagonal Boron Nitride And Their Application On Catalytic Oxidation Desulfurization Of Fuel

With the increasing attention paid to air pollution,relevant regulations on environmental protection and fuel sulfur content have been issued.A large number of organic sulfur compounds in fuel oil will be converted into sulfur oxides?SO_x?,and meanwhile acid rain,fog,haze,and other environmental pollution problems would be generated.In addition,sulfur compounds will lead to poisoning of catalyst,which will indirectly aggravate the generation of air pollution.Therefore,the production of green and clean fuel is very important to maintain healthy life and friendly environment.Nowadays,in view of the shortcomings of traditional hydrodesulfurization technology?HDS?,oxidative desulfurization?ODS?has been widely concerned by researchers because of its mild reaction conditions and highly desulfurization efficiency.Herein,a series of metal-free heterogeneous catalysts with defect structure were designed and constructed based on the study of hexagonal boron nitride?h-BN?.The catalytic oxidation desulfurization performance of molecular oxygen?O₂?was investigated,and the mechanism of catalytic reaction and its structure-activity relationship were systematically explored.The chief research contents and experimental results are as follows:1.The electronic structure of h-BN was regulated by using ternary deep eutectic solvent?DESs?as precursor and template.Carbon doped boron nitride?BCN?catalyst with hierarchical porous structure was synthesized by one-step calcination.The characterization results showed that it has porous structure,and the carbon clusters in BCN catalyst promote the electron delocalization effect and accelerate the activation of oxygen.The prepared BCN-x was used to activate the molecular oxygen catalytic oxidation desulfurization system,and the effect of different reaction conditions on the catalytic oxidation desulfurization performance was investigated.The results showed that the BCN catalyst can reach 98.4%sulfur removal in 4 h under the conditions of m?BCN-1?=50 mg,V?model diesel?=20 mL,V?airflow?=100 mL?min^-1,T=125°C,and the purpose of deep oxidation desulfurization could be achieved.The catalyst also has great catalytic performance for 4-MDBT and 4,6-DMDBT.The order of desulfurization is DBT>4,6-DMDBT>4-MDBT.The BCN catalyst can be recycled 5 times with a little activity decrease.Experimental results revealed that the excellent catalytic activity was found to be originated from an improved electron delocalization.Combined with the density functional theory?DFT?,the improved electron delocalization increased the electronic density of the BCN,promoting the activation of dioxygen.2.A boron nitride catalyst?V-BN?with B and N dual vacancies was synthesized by vacuum calcination.It was confirmed by experiments and the results of the characterization that the B-O and N-H bonds were partially broken and removed in the form of water molecules in the vacuum treatment process,leaving the B and N dual vacancies,and it improved the dissociation and adsorption performance of O₂ as the reactive sites.The prepared V3-BN was used to activate the molecular oxygen catalytic oxidation desulfurization system.The results showed that the DBT could be completely removed in 6 h under the conditions of m?V3-BN?=50 mg,V?model diesel?=20 mL,V?airflow?=100 mL?min^-1,T=125°C.Additionally,it showed outstanding catalytic oxidation desulfurization activity to 4-MDBT.The catalyst can be recycled for 6 times without obvious decrease in activity.The mechanism of the reaction was studied by hot filtration and Electron spin resonance?ESR?characterization.Finally,the oxidation path of DBT on the dual vacancies was further verified by theoretical calculation.3.Boron nitride catalyst?BN-x:y?with high crystallinity,defect and porous structure was prepared by molten salt assisted method.The results showed that the molten salts?KCl,LiCl?functioned as both a soft template and structure-directing agent in the calcination process,improving the crystallinity of boron nitride and the pore structure,producing boron defects and exposing more active sites.The prepared catalyst was used to activate the molecular oxygen catalytic oxidation desulfurization system.The oxidation desulfurization performance under different reaction conditions was investigated.The optimum reaction conditions were as follows:the ratio of molten salt was 4:6,the total mass was 4 g,m?BN-4:6?=50 mg,T=125°C,the reaction time was 8 h,the oxidation desulfurization performance reached over 96.7%,and the goal of deep desulfurization was achieved.The catalyst exhibited excellent catalytic activity for DBT,4-MDBT and 4,6-DMDBT.The order of desulfurization was DBT>4,6-DMDBT>4-MDBT.After recycled 16 times,the activity of catalyst could still reach over 94%.The results of Gas chromatography-mass spectrometry?GC-MS?and ESR showed that the oxidation product was DBTO₂ and the active species was O₂^·-.