Preparation Of Ordered Mesoporous Silica Composites Based On Phosphomolybdate And Catalytic Properties Of Oxidative Desulfurization

The dependence of human life on fuel consumption is increasing,and the emissions and impurities from combustion are not only polluting the atmosphere,but also seriously damaging the ecological environment.Environmental management is still a serious challenge for human survival and industrial production,so it is essential to remove or reduce the organic sulfide in fuel to the limit value to relieve the environmental pressure.Based on the advantages of heteropolyacid-functionalized catalysts in the production of clean fuels with deep desulfurization performance,the synergy between the catalytic active site provided by heteropolyacid and the strong oxidation of hydrogen peroxide is used to catalyze the removal of organic sulfides from dibenzothiophene(DBT),benzothiophene(BT)or 4,6-dimethyldibenzothiophene(4,6-DMDBT)as a model oil fuel.Experiments were conducted to achieve deep desulfurization by oxidative desulfurization technology(ODS).Therefore,the design and preparation of solid acid multiphase catalysts with excellent performance is essential for fuel desulfurization.In this thesis,the Keggin-type phosphomolybdic acid(HPMo)was improved on the conventional preparation process,and thick-pore-walled ordered mesoporous silica composites(HPMo@OMS)functionalized with phosphomolybdic acid were synthesized both as an acidic medium for the synthesis of silica molecular sieves and as a catalytically active species.As a control,ordered mesoporous silica composites functionalized with phosphomolybdic acid(HPMo@SBA-15)were synthesized by the conventional preparation process using hydrochloric acid as the acidic medium;the deep desulfurization performance of the composites was investigated by model oil-catalytic oxidative desulfurization experiments as an exploratory reaction.(1)conventional preparation process: HPMo@SBA-15 composites with different phosphomolybdate contents were prepared in 2 M hydrochloric acid solution with poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)(P123)as the structural templating agent,ethyl orthosilicate(TEOS)as the silica source precursor,and Keggin-type HPMo as the catalytic active site.The pore structure characteristics of the composites,the ordered arrangement of mesopores,and the chemical composition of the composites were characterized by various characterization techniques.The desulfurization performance of the HPMo@SBA-15 composites under the conventional preparation process conditions was investigated by the desulfurization reaction of model oil.In addition,the recycling performance of the composites was also investigated.(2)Improved preparation process: Based on the conventional preparation process,thick-walled HPMo@OMS series composites were prepared using a one-step co-condensation method combined with hydrothermal treatment,using Keggin-type HPMo as both the acidic medium and catalytic active site,P123 as the template agent and TEOS as the inorganic silica source.The morphological characteristics,pore structure parameters,pore wall thickness and chemical composition of the composites were investigated by a series of characterization tools.The catalytic activity of the composites was also investigated in the ODS reaction of model oil in single-factor experiments,which showed that the desulfurization efficiency of the 13.74HPMo@OMS catalyst was up to 100% and the desulfurization performance was still up to 92.5% after ten cycles,and the possible mechanism of the ODS reaction of model oil was proposed;the study showed that the ODS reaction of both catalysts was consistent with the assertion of first-order kinetics.The activation energy of 13.74HPMo@OMS catalyst is lower,which can promote the development of the reaction faster;finally,it was verified that the end product of the ODS reaction is in the form of sulfone.