Functionalmodification Of SBA-15(16) Mesoporous Materialsand Their Application In Heterogeneous Catalysis

Mesoporous materials have attracted considerable attention in the region of optics, electromagnetic and biomedicine due to high surface area, uniform pore size and easily functionalized surface. The research on mesoporous materials is currently changing to the exploitation of their application in catalysis. By choosing appropriate precursors and preparation methods, the functional modification of mesoporous materials has played significant roles in improving the performance of catalytic ability. Combining compositional analysis, structural characterization and catalytic tests, the correlation between structural characteristics and catalytic performance can be performed and the design and preparation of a highly effective catalyst can be optimized, which can provide new insights into the preparation of catalysts.SBA-15 and SBA-16 is a new type of mesoporous silica molecular sieves with uniform hexagonal and 3D channels.The introduction of metal ions in the framework of SBA-15 and SBA-16 is one of the important approaches for its catalytic applications. Nevertheless, it is difficult to directly incorporate metal atom into the framework because SBA-15 and SBA-16 have been generally synthesized under acidic hydrothermal condition that easily induce the dissociation of the M-O-Si bonds. In this paper, SBA-15 and SBA-16 as a matrix, its functional materials (Al/SBA-15,Al/SBA-16,TiO₂/SBA-16,Bi-TiO₂/SBA-15) were synthesized successfully and their catalytic performance in the tert-butylation of phenol and photodegradationRhB are also studied.Two different aluminum-containing mesoporous Al/SBA-15 were prepared by post-synthesis method and direct synthesis method. The results show that Al/SBA-15(DS) possessed higher BET surface area and larger pore volume. The acidic properties were investigated by NH3-TPD and Py-IR. The different synthesis method leads to distinct coordination of Al and intensity of acidity. These results indicated that Al/SBA-15(PG) has more activity ability than the corresponding one synthesized by direct method since they contain more Lewis acid sites and Br?nsted acid sites. Al-containing SBA-16 was prepared by post- -grafting synthesis method. The results indicated that the materials possess 3D caged-like mesostructure and Al was successfully incorporated into the SBA-16 framework. Al/SBA-16 has middle activity ability.The modification of Al controlled the acidity of Al/SBA-15(16) effectively. The interaction betweenSiandAl enhanced the acid content of Al/SBA-15(16). Meanwhile, the modification of Al has also modified the pore structures of SBA- 15(16).In the tert-butylation of phenol, the catalytic activity and reusability of Al/SBA-15(16) were studied. It was found that the highest activity result was obtained under reaction condition: 0.05g Al/SBA-15(16) as catalyst, n(TBA): n(phenol)=5, WHSV=2.5h-1, reaction temperature at 190℃, time for 7h. The catalyst preserved almost their initial catalytic activity after five reuses. The adsorbed energy of phenol and TAB in the channels was calculated by the DFT method. Finally, the alkylation mechanics on Al/SBA-15 and Al/SBA-16 were discussed, respectively.TiO₂/SBA-16 was synthesized by internal hydrolysis method. The results indicated that SBA-16 retained the 3D caged-like mesostructure while TiO₂ located almost inside the mesoporous channels in form of small crystals with anatase structure.and the size of TiO₂ was limited under 5nm. The high specific surface area and pore volume for TiO₂/SBA-16 with 3D mesostructure were prone to have high adsorption capability and easier diffusion to the photo-oxidative. TiO₂ dispersed in form of small crystals with anatase structure and its size was limited by the channel of SBA-16, which could provide more photo-oxidative sites due to quantum effect, leading to improvement of its photocatalytic activity. L-H kinetics model was indicated that an optimal amount of TiO₂ loading is crucial for the photocatalyst. When the loading is too high, TiO₂would gather into larger particles and block the mesopores of SBA-16, leading to decrease of photocatalytic activity. On the contrary, if the loading is too small, the photoactive sites are relatively low, which leads to the increase of average distance from the photoactive sites to the adsorption sites.Bi-TiO₂/SBA-15 was synthesized by two steps synthesis. The high specific surface area and ordered mesoporous channels of SBA-15 are prone to have high adsorption capability and easier photo-oxidative diffusion sites for RhB.The band structure and total density of states of TiO₂ and Bi-TiO₂ were calculated in order to study their electronic structures by the DFT method. It was found that the Bi-TiO₂ in modified SBA-15 catalysts was active centers and the doping of Bi can enhance the photoinduced degradation very significantly. In this system, the electron-hole pairs induced by light irradiation transfer easier and a smaller band gap was also observed for Bi-TiO₂ (from 3.2eV to 1.85eV). This demonstrated that after integration, the electron and hole was separated efficiently, which has played a key role in enhancing the photoactivity.