Hexane cracking catalyzed by MSE-type zeolite as a solid acid catalyst
•Dealuminated MCM-68 showed sufficient activity and coke durability in hexane cracking.•Dealuminated MCM-68 also had higher propylene selectivity than ZSM-5.•When Al-rich MCM-68 was used, significant deactivation due to coke formation was observed.•At higher temperature (650 °C), even dealuminated MCM-68 was deactivated by coke formation.•Modification of external surface with La oxide was an effective way for avoiding coke formation.
MCM-68 (MSE topology) with three-dimensional 12–10–10-ring channel system was focused on, expecting the hybrid character of ZSM-5 (MFI topology) and beta (*BEA topology), as a solid acid catalyst for hexane cracking reaction. The proton form of MCM-68 without dealumination having Si/Al ratio around 12 was deactivated rapidly during the reaction due to heavy coke formation, whereas dealuminated MCM-68 exhibited sufficient catalytic activity and durability to coke formation for hexane cracking at the reaction temperatures from 450 to 600 °C. The dealuminated MCM-68 also had higher propylene selectivity of 45–50% in comparison with other zeolite catalysts such as ZSM-5, mordenite and beta at the reaction temperatures of 450 to 600 °C. Both the MCM-68 catalysts before and after dealumination were regenerated after the reaction at 600 °C to exhibit almost the same performance as the initial catalyst. At higher reaction temperature such as 650 °C, the catalyst was deactivated rapidly mainly due to coke formation again. In order to avoid this deactivation, modification of MCM-68 with lanthanum oxide simply by impregnation was performed. The La-modification mainly deactivated the active site on the external surface and was found to be an effective way for avoiding heavy coke formation to maintain catalytic activity and selectivity to propylene.
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Journal: Catalysis Today - Volume 226, 1 May 2014, Pages 109–116