Hierarchical porous MCM-68 zeolites: Synthesis, characterization and catalytic performance in m-xylene isomerization
Novel hierarchical MCM-68 zeolite materials were successfully prepared by two simple, effective and environmentally friendly methods: H 2 O 2 microexplosion under microwave and NH 3 (aq) treatment. The characterization of the materials with powder XRD , SEM, TEM, N 2 -sorption, and NH 3 -TPD proved that abundant mesopores across zeolite crystals were created while the microporous MSE framework was well preserved. The mesopore volume of hierarchical MCM-68 zeolites is up to 0.19 cm 3 g −1 . The crystallinities of hierarchical ones and microporous MCM-68 are nearly the same according to the XRD result. The acidities of hierarchical MCM-68 are generally lower than their raw materials. Gas-phase isomerization reaction of m -xylene was carried out over these hierarchical MCM-68 zeolites as well as HMCM-68 zeolite under different conditions to characterize the catalytic property of newly prepared hierarchical zeolites. It was found that the m -xylene conversion and disproportionation/isomerization rate ratio were closely related to the created mesopores in hierarchical MCM-68 zeolites under high reaction temperature and low weight hourly space velocity (WHSV). Moreover, these hierarchical MCM-68 zeolites exhibited improved resistance to coke formation compared with HMCM-68.
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