High catalytic performance of surfactant-directed nanocrystalline zeolites for liquid-phase Friedel–Crafts alkylation of benzene due to external surfaces
•Nanomorphic zeolites were synthesized by using structure-directing surfactants.•The catalyst is highly active for liquid-phase FC alkylation reaction.•The catalyst shows high activity and long catalytic lifetime in benzylation reaction.•The high catalytic performance is due to the large amount of external acid sites.
Beta zeolite is known as an efficient catalyst for Friedel–Crafts alkylation. In liquid phase reactions, however, beta zeolite catalyst is often deactivated rapidly. We discovered that the maximum possible catalytic turnovers in benzene alkylation with benzyl alcohol could be increased by six times by using a beta zeolite with a nanosponge-like morphology, in comparison to bulk beta zeolites. The nanomorphic zeolite was obtained using a hydrothermal synthesis method which uses multiammonium surfactants as a meso–micro hierarchical structure-directing agent. The origins of the high catalytic performance were investigated by measuring the catalytic conversions after selectively poisoning acid sites located on external surfaces and in internal micropores selectively. The result indicated that the high catalytic performance was due to the alkylation reactions occurring on external surfaces. External active sites were able to perform the catalytic function even after active sites inside the zeolite micropores were deactivated. Similar results were obtained with other nanomorphic zeolites such as MFI nanosheets, MTW nanosponge and MRE nanosponge.
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Journal: Applied Catalysis A: General - Volume 470, 30 January 2014, Pages 420–426