Organosilane Surfactant-Directed Synthesis Of Hierarchical Zeolites With Meso-/microporosity And Improved Catalytic Performance In Methanol To Olefins

Light olefins?such as ethylene and propylene?are the most important commercial chemical materials and intermediates for chemical industry.With the purpose of catering to the growing demand of light olefins and alleviating the pressure of petroleum exhaustion,the conversion of methanol that can be produced from coal or natural gas to produce light olefins on a large scale,which is so-called as methanol-to-olefin reaction,has been considered as one of the most efficient passways to manufacture light olefins,along with a promising alternative to the petroleum route.Besides reaction conditions,developing an efficient catalyst with high selectivity of light olefins and long catalytic lifetime is the critical factor for the methanol-to-olefin technology,and taking more and more attentions in both academic and industry fields.Due to the unique shape-selectivity,tunable acidity and superior thermal as well as hydrothermal stability,zeolite has been proven to be a remarkably effective catalyst for the methanol-to-olefin reaction.However,the conventional zeolite is restricted by its narrow microporosity?<1.0nm?and excessively strong acidity,leading to intracrystalline diffusion limitation and rapid deactivation,which seriously hinders its practical application in the methanol-to-olefin process.Hierarchical zeolites with multiple levels of porosity are concurrently beneficial for the inherent zeolitic framework and the introduced meso-/macropores to overcome the intracrystalline diffusion restriction.Recent researches are focus on the fundamental study of the efficient synthesis and catalytic implication of hierarchical zeolites with interconnected meso-/microporosity.In this contribution,we demonstrate not only the synthesis of two kinds of hierarchical zeolites?hierarchical SAPO-34 and hierarchical ZSM-5?with interconnected meso-/microporosity via a direct hydrothermal treatment by using the commercial organosilane surfactant TPOAC as a mesopore structure-directing agent but also the fundamental study of their catalytic implication in the methanol-to-olefin reaction.?1?Hierarchical SAPO-34 has a novel nanosheet-assembled structure.The experiment was used to systematically investigate the effect of synthesis conditions?TPOAC/SiO₂ ratios,SiO₂/Al₂O₃ ratios and dynamic hydrothermal conditions?on the structure of hierarchical SAPO-34.The nanosheet-assembled SAPO-34?NA-SP34?,the commercial microporous SAPO-34?CM-SP34?and the nanosheet-like SAPO-34?NS-SP34?were used in the MTO reaction to evaluate their catalytic performance.The results show that the NA-SP34 due to multi-level pore and appropriate acidity,showing a longer catalytic life and higher selectivity to light olefins.The catalytic lifetime is 3.6 times that of the CM-SP34 and about 1.5 times that of the NS-SP34.The ethylene selectivity of NA-SP34 is about 20.5%higher than that of CM-SP34 and 0.9%higher than that of NS-SP34.?2?Hierarchical ZSM-5 has intracrystalline meso-/macropores structure with controllable content.The experiment was used to systematically investigate the effect of amount of TPOAC on the structure of hierarchical ZSM-5.The hierarchical ZSM-5?ZSM-5_T?,commercial ZSM-5?C-ZSM-5?and conventional ZSM-5 without TPOAC?ZSM-5_no_T?were used in the MTP reaction to evaluate their catalytic performance.The results show that the ZSM-5_T due to multi-level pore and the appropriate acidity,exhibiting good catalytic performance in MTP reaction.The catalytic lifetime is almost 7.6 times that of the C-ZSM-5and about 5.4 times that of the ZSM-5_no_T.The propene selectivity of ZSM-5_T is about13.7%higher than that of the C-ZSM-5 and 20.3%higher than that of the ZSM-5_no_T.