Study On Deep Desulfurization By Catalytic Oxidation Coupling In Situ Hydrogenation

Due to the harmful emissions of sulfur oxides(SOx)and sulfate particulate matter(SPM),resulting in air pollution and the formation of acid rain.Therefore,the burning of sulfur-containing fuels in transportation and industry is currently one of the main concerns.In order to achieve the purpose of high selectivity of C-S bond cleavage without reducing the oil yield.In this thesis,porous core-shell nanomaterials and single-atom anchored nitrogen doped redox graphene are used as highly selectivity catalysts for catalytic oxidation coupling in-situ hydrodesulfurization.The synergistic effect between the active center and the carrier simultaneously provides two kinds of reactive sites can achieve deep desulfurization.In this thesis,Porous SiO2@Cu/Ni core-shell nanomaterials were first prepared and analyzed by XPS,high-angle annular dark field scanning transmission electron microscope(HADDF-STEM),H2-TPR,XRD and other methods to characterize it,the results show that the Cu-Ni metal alloy is evenly distributed on the surface of silica,nanoscale core-shell materials possess a little number of micropores and a large number of mesopores.The catalytic performances of the samples were evaluated through the 4,6-DMDBT deep desulfurization.The desulfurization rate and selectivity of catalytic oxidation coupling in-situ hydrogenation at different temperatures reached 100%,the catalyst was reused 10 times and catalytic activity was basically unchanged,At the same time,ICP-OES results show that the catalyst composition is also basically unchanged,indicating that SiO2@Cu/Ni has excellent stability while maintaining excellent catalytic performance,this is because the synergistic effect between the Cu-Ni alloy and the carrier is conducive to deep desulfurization(C-S bond direct fracture)and Cu-Ni metal alloy can suppress metal sintering.Taking advantage of the superiority of single-atom catalysis,single-atom Cu and Ni are supported on nitrogen-doped redox graphene.BET results show that rGO possessed a high surface area of 1362.8 m2·g-1,which is efficient for loading Cu/Ni on the N-rGO surface.Using X-ray adsorption fine structure(XAFS),XRD,XPS,Raman and other methods to characterize the prepared sample Cu/Ni-N-rGO,the result shows that the average distance between two adjacent Cu and Ni atoms is less than 1 nm,Cu and Ni metal single atoms combine with vacancies around nitrogen and exist in the form of Cu-N,Ni-N.Using Cu/Ni-N-rGO as a catalyst for catalytic oxidation coupling in situ hydrogenation cleavage of C-S bonds of 4,6-DMDBT,it was found that under mild conditions,when the single atom loading is 0.8%,the selectivity of 4,6-DMDBT to the corresponding sulfone is about 100%,and the conversion rate reaches 100%.Cu/Ni-N-rGO shows excellent catalytic performance,which is consistent with the calculated apparent activation energy results.Because the synergistic effect between Cu/Ni single atom and rGO promotes oxidation and hydrogenation reactions.Density functional theory(DFT)was used to calculate the microscopic behavior and obtained reaction mechanism of C-S bond breaking during catalytic oxidation coupling in situ hydrogenation.All the structures in the reaction were calculated through optimization,which proved that the optimized structures of SiO2@Cu/Ni and Cu/Ni-N-rGO were consistent with the characterization results.Then conduct a transition state search on the reaction potential energy surface,the transition states have a common virtual frequency around 760.The results show that the C-S bond break of 4,6-DMDBT undergoes two steps of oxidation to sulfone,followed by in situ hydrogenation of the C-S bond cleavage.Compared with the energy required for direct hydrogenation(436.8 kJ/mol)and transition state free energy-940.848(Hartree).Catalytic oxidation coupling in-situ hydrogenation is much easier to achieve deep desulfurization,and the mechanism of C-S bond highly selective breaking was obtained.