Preparation And Catalytic Oxidative Desulfurization Of Axially Coordinated Metal Phthalocyanine

Air pollution has been listed as an early warning problem worldwide,with motor vehicle transportation and the petrochemical industry being a major source of oxysulfide（SOx）,which causes air pollution that causes ozone depletion,acid rain and reduces soil fertility.Desulfurization of petroleum fuels and intermediates is crucial for protecting the ecological environment and human life and health.China,Japan,the European Union and other countries have lowered the sulfur content of gasoline and diesel to 10 ppm.At present,hydrodesulfurization is a commonly used technology in industry,but this technology needs to consume expensive hydrogen as the basis,and needs the support of high temperature and high pressure.In recent years,alternative non-hydrodesulfurization methods mainly include oxidation,biological,extraction,adsorption and other technologies.Among them,oxidative desulfurization does not require expensive hydrogen,has low operating costs and mild application conditions,and has been recognized as a promising technology.Therefore,designing high-activity catalysts and constructing high-efficiency desulfurization systems are the most concerned issues for researchers.Metal phthalocyanines（MPcs）,as biomimetic catalysts,which structures are similar to macrocyclic complexes of porphyrins,have good potential in catalytic oxidative desulfurization,and have attracted much attention in the field of catalysis due to their easy preparation.However,a single metal phthalocyanine easily forms dimers or multimers,which is not satisfactory in terms of catalytic efficiency.Usually,the catalytic activity of phthalocyanine can be improved by changing the central metal atom and peripheral groups of phthalocyanine or through axial coordination,which is of great significance for the application of metal phthalocyanine in the field of oxidative desulfurization.Drawing on the basic structural characteristics of natural biological enzymes,the amino acid components containing O,N and S play an important role in the catalytic activity between metal atoms in metalloporphyrins.In this paper,various kinds of coordinated metal phthalocyanines were prepared by axially coordinating the ligands containing O,N,S with the central metal atom of the metal phthalocyanine.Visible absorption spectroscopy（UV-vis）,Fourier transform infrared spectroscopy（FTIR）and other detection methods were used to analyze the structure of the catalyst.The results showed that the S atom had strong coordination ability with iron phthalocyanine,and the UV absorption peak shifted significantly.The catalytic activity of the catalyst was tested by oxidative desulfurization experiments with green ethanol and aqueous solution（volume ratio of 9:1）as extractant and hydrogen peroxide（H₂O₂）as oxidant.The results show that iron phthalocyanine/4-mercaptopyridine（Fe Pc/4-Mpy）has good catalytic oxidation desulfurization performance,which is consistent with the conclusion of the UV-vis absorption peak.When the catalyst dosage is 10 mg,the temperature is 30°C,the oxygen-sulfur ratio is 40,and the volume ratio of solvent and oil is 2,the simulated oil with 200 ppm sulfur content can be reduced to less than 10 ppm in the reaction under normal pressure for 120 min.Through the electron paramagnetic resonance（EPR）test,the dimethyl sulfoxide（DMSO）oxidation experiment proved that the hydrogen peroxide in the system will undergo homo-and hetero-fission to generate hydroxyl radicals（·OH）and high-valent iron-oxo species（Fe（IV）=O）,respectively.And the coordination of S atoms is conducive to the heterocleavage of O-O bonds to generate Fe（IV）=O,thereby improving the oxidation ability and selectivity of the desulfurization system.In order to further improve the catalytic oxidative desulfurization performance of iron phthalocyanine,F atom with strong electron withdrawing property was introduced to replace the H atom of the outer ring of phthalocyanine.The introduction of F atom is beneficial to reduce the energy of molecular orbital and improve the stability of the catalyst,and the F atom-substituted iron phthalocyanine is more likely to form an oxygen bridge structure,thereby improving its catalytic performance.Similarly,a new axial coordination catalyst was synthesized by simulating the structure of natural P450 enzyme and using 4-mercaptopyridine to coordinate axially with Fe Pc F₁₆-O-Fe Pc F₁₆.The structure was also characterized and analyzed by EDS,UV-vis,FTIR and other methods,which proved the existence of oxygen bridges in the catalyst and the coordination of the iron atom in the center of the phthalocyanine with the S atom of the sulfhydryl group.Secondly,using dibenzothiophene（DBT）as the main target substrate,a DBT solution with a sulfur content of 200 ppm was prepared,and a solution with a volume ratio of ethanol to water of 9:1 was used as the extractant.The effects of oxygen-sulfur ratio,temperature,p H value,solvent-oil ratio,different sulfur content and different substrates on the desulfurization efficiency of the catalytic system were studied.Under the conditions of temperature of 30°C,extraction agent of 10 m L,oxygen-sulfur ratio of 20,and agent-oil ratio of 2:1,the desulfurization rate can reach 99.7%within 30 min.Through electron paramagnetic resonance spectroscopy test,dimethyl sulfoxide oxidation experiment,N,N-diethyl-p-phenylenediamine sulfate（DPD）oxidation color development experiment and density functional theory（DFT）,which proved that the main active substance of oxidative desulfurization is Fe（IV）=O.In this paper,a metallophthalocyanine structure with axial coordination was constructed by simulating the structural properties of natural P450 enzymes.It provides basic data for the development of catalysts for high-efficiency desulfurization and has good potential in industrial applications.