Synthesis Of Hierarchical Zeolites Without Extra Templates And Its Catalytic Applications

As the traditional microporous zeolites have good shape-selective, strong acid, large BET surface area and good hydrothermal stability/thermal stability, they are now widely used in adsorption/separation, petrochemical field and other fields. However, the micropores could cause diffusion limitation of bulky molecules in catalytic reaction, thereby affecting the catalytic performance of microporous zeolites. Recently, zeolites with different porosity or hierarchical structure have been demonstrated to be a good way to solve diffusion limitation problems of bulky molecules within micropores.Nowadays, a large number of synthetic strategies have been developed to synthesize zeolites with hierarchical structure. However, only few methods could be scaled up. The purpose of this paper is to use an innovative and scalable way to synthesize hierarchical zeolites. The synthesis mechanism of mesopore and the introduction of mesopores on the bulky molecules reaction have also been studied.Herein, we use quasi-solid phase conversion method to synthesize nano-sized zeolites with hierarchical structure by just one step, and additional template is not added during the synthesis process. The as-synthesized samples are characterized by N2absorption-desorption, scanning electron microscope and other characterization methods. The results have shown that the critical factor for synthesis of hierarchical zeolites is the water content of zeolite precursors. The synthesis result of zeolite precursors with low water content will be amorphous aluminosilicate; while zeolite precursors with high water content will result in the formation of microporous zeolite Beta.The mesopore distribution could be controllable by changing the synthesis conditions, such as crystallization time, Si/Al, different SiO2, TEA+content, crystallization temperature, drying temperature, etc. The experiment also prove that the first step is the growth of microporous zeolite Beta and then the formation of the mesopore in the synthesis process. The mesoporous pore size of hierarchical zeolite Beta is closely related with the mesoporous pore size of SiO2. TEA+play two roles in the synthesis process, on the one hand, it induces the formation of micropore; on the other hand, it limits the growth of crystals. Si/Al, drying temperature and crystallization temperature should have a suitable rang, the higher Si/Al ratio will lead to the disappearance of the mesopore, while the higher drying temperature will cause the formation of amorphous aluminosilicate.Compared with the conventional microporous zeolite Beta, hierarchical zeolite Beta exhibits good stability in the alkylation reaction of benzene with propylene, and the hierarchical zeolite Beta also shows a higher conversion of tri-butylbenzene as well as a higher selectivity of sec-butylbenzene in the transalkylation reaction of benzene with tri-butylbenzenes and di-butylbenzenes.