Synthesis And Characterization Of Mesoporous Materials With Strong Acidity

Since mesoporous silica meterials M41S with uniform size and high surfacearea(>1000 m2/g) were reported by Mobil company, much attention has beenattracted because of the potential application in catalysis, adsorption and separation,assembly etc. But during the following research it is found that the mesoporoussilica materials show very poor hydrothermal stability and weak acidity. So theirwide application is limited. In order to improve their hydrothermal stability andacidity, a large number of work have been done. And then it is known that poorhydrothermal stability and weak acidity are attributed to the amorphous nature of themesopore wall in mesoporous silica materials. So it is supposed that if the porewall of mesoporous silica materials is crystalline similar to zeolites, theirhydrothermal stability and acidity should be improved greatly. Recently, professor Xiao et al. have prepared successfully a series of novelMAS mesoporous materials by self-assembly of zeolite nanoculsters. Althoughthese mesoporous materials exhibited no crystalline phase similar to zeolites, theirhydrothermal stability and acidity have been improved greatly, compared with - i -Jilin University Ph.D. Thesis Abstractconventional mesoporous silica materials. It is proposed that the improvement ofhydrothermal stability and acidity should be attributed to the existence of zeolitenanoclusters in these mesoporous materials. But it is very difficult how to provethem. Here, we designed a skillful pattern to characterize the micropores in thesemesoporous materials. The pattern is that, at first these mesoporousaluminosilicates are treated by bulky basic organic molecular (DBHC). In this case,the acidic sites in mesopores are killed and the acidic sites in micropores whose sizeis less than molecular diameter of DBHC are still active. And then we tested theircatalytic activity by using catalytic reactions of probing molecules with variousdiameters in order to confirm whether the materials contain micropores and whichtypes of micropore the materials contain. For example, by this method we confirmthat MAS-7 contains micropores whose size is similar to that of Beta and MAS-9contains micropores whose size is similar to that of ZSM-5. It is well known that ordered mesoporous all-silica materials have almost noacidity. After Al atoms were introduced into the framework of the silica materials,the samples showed weak acidity. Recently, those mesoporous materials preparedby self-assembly of zeolite nanoclusters have made further improvement on theacidity, but it is still not enough. Here, we combined the mesoporous silicamaterials with superacids materials in order to improve the acidity of the mesoporousmaterials. And then sulfated zirconia was supported in mesoporous silica materials.Cumene and 1,3,5-triisopropylbenzene cracking reactions show that the mesoporoussilica materials supported sulfated zirconia have stronger acidity than Al-MCM-41and MAS serials of mesoporous meterials. Although the acidity of mesoporous silica materials has been greatly improvedby means of that solid superacids were supported in mesoporous materials, there arestill some questions such as the loss of sulfated zironia, the blockage of pore - ii -Abstract Jilin University Ph.D. Thesischannels, the obvious decrease of the surface area and the acidity. So it is expectedthat mesostructured sulfated zirconia can be directly prepared. Here, we haveprepared successfully mesostructured sulfated zirconia (MSZ-5) with strong acidityand high surface area by using the tri-block copolymer as a surfactant. The sampleshows high catalytic activity on the n-butane isomerization. Furthermore, it is found that the mesostructured sulfated zirconi...