Synthesis,Characterization And Catalytic Properties Of Mesostructured Materials Of Different Heteroatoms

Inorganic materials are the most promising in green catalysis materials;exploitation of green catalysis materials is related to inorganic materialsresearch. Microporous or mesoporous materials are more and more graduallystudied by scientific researchers. Microporous zeolite materials with uniformand molecular-size pores have been widely used in many fields such asion-exchange, adsorption and separation, and industrial catalysts. However,they cannot effectively deal with large molecules due to the limitation of themicropore size. Mesoporous molecular sieves show great potentialapplications and attract much attention because of their uniform and largermesopores.With the great progress gained in the field of the mesoporous materialsresearch, the syntheses of mesoporous materials are not limited in thealkaline media. Synthetical SBA-15 series materials in strong acid mediahave more advantages than the materials (MCM-series materials) synthesizedin alkaline media, such as the thicker mesoporous pore walls, the larger poresand the ordered channels, and good hydrothermal stability. However, thesynthesis of heteroatom contained SBA-15 is difficult, because the metalswill only exist in the cationic form other than their corresponding oxo speciesin the strong acid. Consequently they can not enter silica framework bycondensation with silicon species, therefore it is diffcult to prepareheteroatom-containing mesoporous silica under strong acidic media directly.Generally, there are two kinds of methods for the incorporation of heteroatom,"direct-synthesis" and "post-synthesis". For "direct-synthesis" method, theamount of the heteroatom introduced into the mesoporous walls is littlethough there may be a large amount of the heteroatom added in the initial gel.For "post-synthesis" method, the amount of heteroatom introduced is larger.However, the operation is so complicated, sometimes glove box is necessarybecause some metals are easy to oxygenate when they are exposed to waterand oxygen. Once the oxygen is formed, it will jam the channels and limittheir application. On the other hand, the procedures are easy to destroy thestructure of the ordered mesoporous materials.We find that heteroatoms can be effectively introduced into theframework of mesoporous silica by using "seed solution" as precursors. Thisis because heteroatom species have been fixed in the framework of the zeoliteprimary units when the seed solution is prepared and with the self-assemblyof the zeolite primary units surrounding the surfactant, heteroatom species aredirectly introduced into the mesostructure. Herein FeS-1,VS-1 or CuS-1precursors are loaded and highly dispersed on the surface of mesoporousmaterials SBA-15,MCM-41 or SiO2 by impregnating method. The XRDpattern shows that the samples have still retained mesoporous structureassociated with the hexagonal symmetry. IR spectrum of the samples exhibitsan obvious band at 550cm-1. The band at near 550cm-1 is similar to that offive-membered rings in microporous zeolites. The results suggest that zeoliteprimary and secondary building units are highly dispersed on the samples. Inthe phenol oxidation reaction, the samples exhibit high catalytic activities,which are comparable with that of TS-1;in styrene epoxidation reaction,Cu/SBA-15 shows high activity and selectivity, we find preferabletemperature , preferable precursors and preferable TBHP/styrene caneffectively improve conversion and yield of styrene oxide.In addition, we synthesize mesoporous MCS-9 and MVS-9 by usingzeolite CuS-1 and VS-1 seed solution as inorganic precursor respectively andtriblock copolymer surfactant as template. The XRD pattern shows that thesamples have still retained mesoporous structure associated with thehexagonal symmetry. IR spectrum of the samples exhibits an obvious band at550cm-1.+The band at near 550cm-1 is similar to that of five-membered ringsin microporous zeolites. The results suggest that the samples have zeoliteprimary and secondary building units. Catalytic results of phenol oxidationand styrene epoxidation show that MCS-9 is more active than mesoporousMVS-9 and MFS-9.