Study On Functionalized SBA-15Molecular Sieve For Cycloaddition Reaction

As a newly reported silica mesoporous material, SBA-15has regular pore arraywith uniform pore diameter, much higher hydrothermal stability than MCM-41, highsurface area and the surface silanol groups of chemically inert but allow irreversiblesurface modification by reaction. In this dissertation, combining the functionalizedmethods of metal backbone doping and organic groups surface modification, wedemonstrate a synthetic procedure to generate a successful cohabitation of acidic sitesand basic sites in SBA-15: using metal centers with acid sites, and the acidic centershould be located in the framework walls or the surface of the mesoporous channel;the basic groups should be introduced in the channel pore by postgrafting of organicbases. Several acid-base bifunctionalized mesoporous silica materials have beensynthesized and characterized by means of XRD, Nitrogen physical adsorption, TEM,and TPD analysis, et al. The cycloaddition reaction of carbon dioxide and epoxideswas employed to evaluate the catalytic activity of the functionalized materials. Themain contents were as follows：Ordered mesoporous metal-doped silica materials Ti-SBA-15and Ti-Zr-SBA-15were synthesized using one-pot hydrothermal synthesis methodology in acidiccondition. The characterization results indicated that the interaction of Ti4+and Zr4+have effectively restrained the aggregation and crystallization of metal oxides in thesurface of materials, and significantly increased the actual amount of two metals ofthe framework. Ti and Zr were incorporated into the SBA-15framework as isolatedspecies, and the typical mesoporous structure properties were maintained in themesoporous material with （Ti+Zr）/Si ratio of15%. The results of NH₃, CO₂-TPD andpyridine adsorption indicated the acidic sites and basic sites coexist in the mesoporousmaterials.Combining the functionalized methords of backbone doping and organicmodification, bifunctional mesoporous catalysts containing acidic site in theframework and a basic site in the pore of SBA-15had been synthesized bypost-grafting of aminepropyl （-NH₂）, imidazole （-Im） and adenine （-Ade）. Ethanolwas used as solvent at the first time in the processes of imidazole and adeninefunctionalized, avoiding the use of methylene chloride, DMF and acetonitrile and other toxic organic solvents, and simplified the synthesis step. The characterizationresults indicated that the successful introduction of organic basic groups inTi-SBA-15, and the functionalized samples can possess the ordered mesoporousstructure properties. Because of the space hindrance between the acidic sites and theimmobilized adenine group, they can cohabit independently without mutualdestruction. Therefore, a cooperative catalysis originated from the acidic and basicsites of Ti-SBA-15-Ade showed a higher catalytic performance in catalyzing thesynthesis of cyclic carbonates via the coupling of carbon dioxide with epoxides andgood reusability.Acid-base bifunctionalized mesoporous silica material Ti-Zr-SBA-15-IL wasprepared by a one-step synthesis in a self-generated acidic environment introducingmetal titanium and zirconium, and a post-grafting method which functionalized by1-Methyl-3-propylimidazolium chloride （MPImCl） ionic liquid. The characterizationresults indicated that the titanium and zirconium species were efficiently introducedinto the backbone and ionic liquid groups are anchored into the channel by thecovalent Si-C bond. The functionalized materials could keep mesoporous frameworkwell and a cooperative catalysis originated from the acidic metal centers and basicionic liquid of the bifunctional heterogeneous catalyst showed a higher catalyticperformance than siliceous SBA-15-supported imidazolium based ionic liquid did incatalyzing the synthesis of cyclic carbonates via the coupling of carbon dioxide withepoxides. Furthermore, the catalyst Ti-Zr-SBA-15-IL can be reused for4timeswithout significant decrease of activity.