| The catalytic dehydrogenation of propane has acquired great attention due to the increasing demand of propylene. ZSM-5 zeolite as an important material is widely applied in the support of the catalyst of propane dehydrogenation. However, for the propane dehydrogenation, many efforts have been made to enhance the propylene yield by developing new catalysts with high catalytic performance and stability. In this paper, the physiochemical properties of ZSM-5 zeolite have been modified by the addition of Sr promoter, changing the structure and crystal shapes of ZSM-5 zeolite. Besides, the new core-shell structure of ZSM-5@MgAl2O4 (Z@MA) has been synthesized. Moreover, we synthesized the new structure of SBA-15@MgAl2O4 (S@MA) and compared the different between two catalysts which supported on the Z@MA and S@MA.1. Compared with PtSn/ZSM-5 catalyst, PtSnSr/ZSM-5 exhibited higher catalytic activity and selectivity to propylene. The effect of Sr addition to PtSn/ZSM-5 catalyst on the catalytic performances of propane dehydrogenation was studied. Results showed that the addition of Sr (1.2 wt%) could not only modify the characteristics of both acid and metal function, but also reduce the amount of coke deposition. The results were opposite when the Sr was over-loaded. By the co-effect of Sr and Na, the catalyst of PtSnSrNa/ZSM-5 had the best catalytic performance in terms of propane dehydrogenation and stability.2. The new structure of ZSM-5@MgAl2O4 was synthesized by the sol-gel method. By the introduction of Mg2+, Al3+ into the framework of ZSM-5 zeolite, the amounts of acid sites were significantly decreased, especially for the strong acid site. As the weight ratio of MgAl2O4/ZSM-5 is equal to 3, the Sext was increased, the dispersion of platinum particles was improved, and the effects between metal and support were promoted. PtSnNa/Z@MA-3 exhibited the best catalytic performance in terms of propane dehydrogenation and stability. Moreover, the coke deposit on the catalyst of PtSnNa/Z@MA-3 was highly suppressed, and even the coke deposit on the metal would migrate to the external surface of the support.3. ZSM-5 zeolite with surface defects (abbreviated henceforth as ZQ) was prepared by the hydrothermally synthesis method and applied for the synthesis of propane dehydrogenation catalysts. The results showed that the pore structure was changed, the acid content was decreased, and the surface properties were promoted by the surface defects in ZQ. Besides, these modifications on zeolite greatly improved the capacity of catalysts to accommodate coke. The coke deposit on PtSnNa/ZQ would migrate from active metal to the support. Furthermore, many Pt particles could be located in the defects of catalyst. Thus the further agglomeration of Pt particles during reaction process was prohibited. As expected, for the catalyst of PtSnNa/ZQ, the catalytic performance of propane dehydrogenation to propene and the stability of the catalyst were significantly promoted.4. A new zeolite with flower-shaped crystals (abbreviated as ZPA) as a catalyst support was synthesized through hydrothermal preparation method. Effects of the crystallization time on the materials were discussed. In particular,3-day-long crystallization resulted in flower-shaped crystals with the smallest crystal size and the largest surface area compared with other samples. The formation of flower-shaped crystals directly influenced the physiochemical properties of ZPA material, and the particle size of platinum on PtSnNa/ZPA was highly decreased. Due to these modifications, the capacity of the catalyst supported on ZPA to accommodate coke was highly improved and the coke deposit on PtSnNa/ZPA was migrated from active metal to the support. The catalytic performances of propane dehydrogenation to propylene and the stability of PtSnNa/ZPA catalyst were significantly promoted.5. Combining with the large surface area of SB A-15 and the high hydrothermal stability and low acidity of MgAl2O4, the core-shell structured SBA-15@MgAl2O4 (abbreviated as S@MA) was synthesized though sol-gel method. The results showed that the pore structure was changed, the acid sites were introduced and the surface properties were improved by the construction of the core-shell structured S@MA. Moreover, in PtSnNa/S@MA, these modifications not only decreased the size of surface Pt ensembles, but also changed the interfacial character between metal and support. Although PtSnNa/Z@MA showed the higher catalytic activity of propane dehydrogenation, the catalyst of PtSnNa/S@MA had better catalytic stabilitydue to the high capacity of the coke. |
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