Friedel-Crafts alkylations over hierarchical zeolite catalysts

Hierarchical mesoporous ZSM-5 (M-ZSM-5) was prepared using amphiphilic organosilane as a mesoporous structure-directing agent, and characterized by XRD, N₂ sorption, ²⁷Al and ²⁹Si MAS NMR spectroscopy, and 2-methyl-2-pentene isomerization. The XRD and N₂ sorption data indicate that M-ZSM-5 is a mesoporous material with ZSM-5 framework. ²⁹Si MAS NMR spectroscopy revealed that M-ZSM-5 was highly crystalline, like conventional ZSM-5. ²⁷Al MAS NMR spectroscopy showed that most of the aluminum atoms were in tetrahedral coordination and 2-methyl-2-pentene isomerization exhibited that M-ZSM-5 possessed strong acidity similar to conventional ZSM-5. The benzylation reaction of benzene by benzyl alcohol was used to evaluate the catalytic reactivity of the hierarchical zeolite catalyst in Friedel-Craft alkylations. The results showed that M-ZSM-5 had a much higher catalytic activity than conventional ZSM-5. The apparent rate constant for M-ZSM-5 is 23 times larger than that for conventional ZSM-5. Moreover, the catalyst could be reused and maintain the initial activity even after three cycles. These results indicate that hierarchical zeolites have potential application in Friedel-Crafts alkylations, especially of large molecules.