Study On Preparation Of Mesoporous Silica Supported Molybdenum Oxide Catalyst And Catalytic Oxidative Desulfurization Of Model Oil

In recent years,the pollution of the global environment caused by the combustion products of fossil fuels is becoming more and more serious.Therefore,the production of green fuel oil is of great significance for reducing environmental pollution and protecting the ecological environment.Because catalytic oxidative desulfurization has high desulfurization efficiency and effective removal of thiophene and its derivatives which are stubborn for hydrodesulfurization.In this dissertation,the research progress of fuel oil oxidative desulfurization was reviewed,three different mesoporous silica supported molybdenum oxide-based catalysts were prepared.,then the catalysts were applied in H₂O₂ system to catalyze the desulfurization of benzothiophene（BT）,dibenzothiophene（DBT）and 4,6-dimethyldibenzothiophene（4,6-DMDBT）model oil.The main research conclusions were as follows:Firstly,the mesoporous silica supported molybdenum oxide catalyst Mo O₃/Si O₂ was prepared by in situ synthesis.It was employed for catalytic oxidative desulfurization.When the reaction temperature was 60℃,the desulfurization rates of DBT,BT and 4,6-DMDBT model oil were close to 100%after 12 min,24 min and 12 min,and the rate constants of these reaction were 0.584 min^-1,0.162 min^-1 and 0.503 min^-1,and the apparent activation energies of these reaction were 58.52 k J/mol,59.50 k J/mol and 59.20k J/mol.After the catalyst was recovered and regenerated,the desulfurization rate of DBT,BT and 4,6-DMDBT model oil was only 28.9%,0%and 17.1%after repeated use of catalytic oxidation for three times.The catalyst had a relatively long reaction time and poor stability.Regarding the issue above,the template P123 was added into the preparation process to control the pore structure of the catalyst,and the catalyst P123-Mo O₃/Si O₂ was prepared.After P123 was added,the specific surface area,average pore diameter and pore volume of the catalyst were increased.It was employed for catalytic oxidative desulfurization.When the reaction temperature was 60℃,the desulfurization rate of DBT,BT and 4,6-DMDBT model oil were close to 100%after 8 min,15 min and 8 min,and the rate constants of these reaction were 1.033 min^-1,0.306 min^-1 and 0.619 min^-1,and the apparent activation energies of these reaction were 51.61 k J/mol,57.01 k J/mol and 55.79k J/mol.After the catalyst was regenerated and regenerated,the desulfurization rate of DBT,BT and 4,6-DMDBT model oil was only 4.8%,3.5%and 4.2%,respectively.The addition of template P123 effectively improved the catalytic activity of the catalyst and shorten the reaction time,but the stability was still poor.In order to further improve the catalytic activity of the catalyst and enhance the reusability of the catalyst,the modifier cerium chloride heptahydrate was added into the preparation process to perfect the surface structure of the catalyst,and the catalyst P123-Ce/Mo O₃/Si O₂ was prepared.It was employed for catalytic oxidative desulfurization.When the reaction temperature was 60℃,the desulfurization rate of DBT,BT and 4,6-DMDBT model oil were close to 100%after 5 min,12 min and 6 min,the rate constants of these reaction were 1.416 min^-1,0.283 min^-1 and 1.056 min^-1,and the apparent activation energies of these reaction were 46.67 k J/mol,56.23 k J/mol and 55.54 k J/mol.The addition of the modifier cerium chloride heptahydrate further improved the catalytic activity of the catalyst.The desulfurization rate of the catalyst could still reach 94.0%,63.0%and 77.9%after repeated use for five times;the catalytic activity of the three catalysts was arranged in the following order:P123-Ce/Mo O₃/Si O₂>P123-Mo O₃/Si O₂>Mo O₃/Si O₂;The catalytic activity of the catalyst for the three sulfur containing compounds was arranged in the following order:DBT>4,6-DMDBT>BT;the sulfur containing compounds were all oxidized to their corresponding sulfones after the catalytic oxidation desulfurization reaction,and the sulfones were adsorbed by catalyst surface,the model oil after the reaction contained almost no sulfur compounds.The catalytic activity and reusability of the catalyst are significantly improved.