首页|Regulating the distribution of acid sites in ZSM-11 zeolite with different halogen anions to enhance its catalytic performance in the conversion of methanol to olefins
Regulating the distribution of acid sites in ZSM-11 zeolite with different halogen anions to enhance its catalytic performance in the conversion of methanol to olefins
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Purposive regulation of the spatial location and distribution of acid sites in a zeolite catalyst,though still rather challenging,has proved to be an effective measure to enhance its performance in the conversion of methanol to olefins(MTO).Herein,a series of ZSM-11 zeolites were synthesized using different sodium halides(with tetra-butylammonium hydroxide(TBAOH)as the structure-directing agent); the effect of halogen anions(CI~-,Br~-and I~-)in the synthesis gel on the Al siting and thereon the spatial location and distribution of acid sites in the ZSM-11 zeolites as well as their relation to the catalytic performance in MTO was elaborately investigated.The results indicate that for the synthesis of high Si/Al ratio ZSM-11 zeolites(Si/Al>60),the CI~-anions present in the synthesis gel can induce more Al atoms siting on the external surface of ZSM-11 crystals,thereby leading to a short catalytic lifetime in MTO due to the rapid coke deposition.In contrast,larger Br~-or I~-anions in the synthesis gel,owing to their stronger covalent interaction with the TBA~+ cations,may moderate the formation of crystal silicate nuclei and lead to a uniform distribution of Al species in the inner straight channels,which can effectively suppress the surface coke deposition and inhibit the aromatic-based cycle for MTO.As a result,the high Si/Al ratio ZSM-11 zeolites obtained with Br~-or I~-in the synthesis gel exhibit much better catalytic stability in MTO and higher selectivity to propene and butene,in comparison with the ZSM-11 counterpart synthesized using Cl".These results help to clarify the relation between the catalytic performance of ZSM-11 in MTO and the location of acid sites and thus bring forward a facile strategy to enhance the catalytic performance of zeolites through purposively regulating the spatial distribution of acid sites.
Methanol to olefinsZSM-11 zeoliteAcid sites distributionHalogen anionsAluminum sitingZeolite framework
Kai Yuan、Xiangyu Jia、Sen Wang
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State Key Laboratory of Coal Conversion,Institute of Coal Chemistry,Chinese Academy of Sciences,P.O.Box 165,Taiyuan,Shanxi,030001,PR China
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