Preparation, Characterization And Application Of Hierarchical Porosity Monolith

Zeolite monoliths with hierarchical porosity have attracted much attention due to their potential applications in the industrial fields. These materials have been proven to be the promising catalysts because the incorporation of interconnected macropores in microporous materials not only greatly increases mass transfer but also makes reactant easier access to the active sites, which favors the improvement of the catalytic performance. In this dissertation, we first prepared meso/macroporous aluminosilica monoliths, titania-silica monoliths and silicoaluminophosphate monolith by phase separation in sol-gel process, and then by the dry gel conversion technology, we got zeolite monoliths with hierarchical porosity. Finally, we investigated the catalytic performance of these zeolite monoliths with hierarchical porosity respectively. The main results in this dissertation are shown as follows:1. Aluminosilica monoliths with bicontinuous macropores and ordered mesopores were successfully prepared by phase separation combined with template technique. The bimodal meso-macroporous structure can be respectively controlled through adjusting PEG amount, surfactant amount and surfactant kinds. The aluminosilica monolith with bicontinuous macropores and ordered mesopores showed best performance on the cracking 1,3,5-Triisopropylbenzene reaction compared with other aluminosilica monolith.2. Bicontinuous beta zeolite monolith was prepared by the dry gel conversion technology. The results showed that the amorphous skeletons of the original silicoalumin monolith are partly converted into zeolite structure with maintenance of the bicontinuous structure. Moreover, catalytic performance of the hierarchical beta zeolite prepared via dry gel conversion method has higher activity and better stability for the transalkylation reaction in the liquid catalytic circumstance.3. Titania-silica monoliths with bicontinuous macropores and interconnected mesopores were successfully prepared by sol-gel method and vapor-phase grafting method. The hydrophobicity of the titania-silica monolith was improved after silylation. The results showed the titania-silica monolith with hierarchical porosity modified by silylation showed enhanced catalytic activity in the epoxidation of cyclohexene compared with SBA-15 silylanized.4. TS-1 zeolite monoliths with bicontinuous macropores were prepared by the dry gel conversion technology. TS-1 zeolite crystals were formed and the bicontinuous macroporous structure was not destroyed during the crystallization process, and the Ti species were incorporated into the skeletons of TS-1 zeolite monolith with tetrahedral coordination. Moreover, catalytic performance of the hierarchical TS-1 zeolite monolith prepared via dry gel conversion method has higher activity and selectivity due to the existence of bicontinuous macropores and interconnected mesopores, which make zeolite crystals fully exposed and make materials possess better mass transfer.5. Silicoaluminophosphate monoliths were prepared by phase separation in sol-gel process. The results showed that the macropore morphology and macropore size distributions could be controlled by adjusting PEO amount, PO amount and aging temperature.6. Hierarchical SAPO zeolite monoliths with different morphology were prepared by the dry gel conversion technology. The results showed that P/Al molar ratios and crystallization methods have an important effect on zeolite morphology; Si/Al molar ratios influence the acidity of zeolite; crystallization time and crystallization temperature determined the formation and growth of crystalline nucleus; template kinds work on zeolite type.7. The catalytic activity of hierarchical SAPO-34 zeolite monoliths with different morphology was investigated for methanol conversion to light olefins (MTO) reaction. The results showed that hierarchical SAPO-34 zeolite monoliths have higher catalytic activity and better stability compared with the conventional SAPO-34 zeolite. Moreover, it is also found by comparison that the hierarchical SAPO-34 with sphere-shaped morphology exhibits higher catalytic activity and the hierarchical SAPO-34 with layer-shaped morphology possess better stability.