The Synthesis Of Hierarchical Porous Silica And Silica/Carbon And Their Applications In The Production Of Clean Diesel

Bimodal mesoporous silica and micro-me soporous silica/carbon were synthesized and applied in the production of clean diesel,including the adsorption of alkali nitrogen compounds, the oxidative desulfurization and hydro-de-aromatization.Bimodal mesoporous silica (BMMS) with two coexisting phases was synthesized by co-hydrothermal aging(CHA) route. The effect of synthetic conditions on the structure and morphology of BMMS were studied with XRD, N2 adsorption-desorption, TEM and SEM. The thermal dynamics and the kinetics of alikali nitrogen removal by adsorption on BMMS were studied with SBA-15 as the reference. It was shown that inkbottle-shape semi cubic small mesopores(2 nm -5 nm) and hexagonal arranged cylindrical large mesopores(3 nm-7 nm) existed together in BMMS.Longer stirring time after mixing led to wider distribution of pore size,and the mass ratio between P123 and F127 was an effective way to tailor the pore parameters of BMMS. The pH value should be lower than 3.0. The synthesis mechanism was suggested, the reaction step in the CHA route is decisive on the pore size of BMMS and the co-hydrothermal aging plays the key role in the formation of BMMS.The thermal dynamic and kinetic researches were performed on the adsorption of alkali nitrogen compounds on BMMS. The thermal dynamic research results showed that the Freundlich model described the adsorption of the alkali nitrogen on both BMMS and SBA-15 better than the Langmuir model. The fact that ?H of these two processes is less than 40 kJ·mol-1 suggests that physical adsorption dominates the process, and a negative ?G implies they are spontaneous processes. A pseudo-second-order kinetic model could describe the adsorption of alkali nitrogen compounds on both materials quite well, based on which it could be concluded that BMMS would remain active under lower temperature than SBA-15 due to a lower activation energy.BMMS was modified with amphiphilic (C19H42N)3(PMo12O40)(CTA-PMO) by a two step impregnation method. The catalyst CTA-PMO/BMMS was characterized by XRD, N2 adsorption-desorption, FTIR, 31P-NMR, 29Si-NMR and TEM. It was shown that the catalyst had typical bimodal mesoporous structure, among which the small mesopore diameter was about 3.0 nm and the large mesopore diameter was about 5.0 nm. The chemical interaction existed between Keggin structure and the silica group of BMMS, the chemical interaction also existed between C19H42NBr and H3PMo12O40. Compared with the monomodal porous H? and SBA-15 modified with CTA-PMO, CTA-PMO/BMMS showed higher catalytic activity in the oxidative conversion of dibenzothiophene (DBT), where the maximum desulfurization rate reached 93.7% after extraction, and the catalyst could be separated by filtration and reused directly. When the straight run diesel yield reached 95%, the desulfurization rate was 85%, in this situation the catalyst can be reused after the solvent's washing. The catalytic oxidative desulfurization mechanism was proposed and proved, the catalyst could transfer the active oxygen from H2O2 to the sulfur compounds and the amphiphilic active composites were beneficial for the reaction.The meso-microporous silica-carbon catalysts Pt/OMC-X (X stands for HY? H? or HZSM-5) were synthesized with the solvent evaporation self-assembly and roasting reduction method. The structure and properties of the catalysts were characterized with XRD, N2 adsorption-desorption, SEM, TEM, XPS and NH3-TPD. Effects of the types of zeolites in Pt/OMC-X on the hydro-de-aromatization performance and sulfur tolerance were studied with the naphthalene as the model aromatics. It was shown that the addition of HY zeolite increased the acidity of the mesoporous carbon and that Pt particle could disperse finely on the surface of the supports with an average particle size of 5.0 nm. Pt/OMC-HY showed good catalytic activity, selectivity and sulfur tolerance. The conversion of the naphthalene was higher than 98% and the selectivity for decalin was about 95%. It was concluded that the strong acidic sites of HY not only play a key role for good high activity and selectivity but also promoted the electron transfer of Pt. The electron deficient state of Pt could restrain the formation of Pt-S bond, thus the sulfur tolerance of the catalyst was improved.