Direct synthesis of hierarchically structured MFI zeolite nanosheet assemblies with tailored activity in benzylation reaction

The MFI zeolites with nanosheet assemblies morphology were prepared by a seed-assisted strategy using specially designed bolaform surfactant [C 6 H 13 -N + (CH 3 ) 2 -C 6 H 12 -N + (CH 3 ) 2 -(CH 2 ) 12 -O-(p-C 6 H 4 ) 2 -O-(CH 2 ) 12 -N + (CH 3 ) 2 -C 6 H 12 -N + (CH 3 ) 2 -C 6 H 13 ] [Br − ] 4 (C 6-12-diphe ) as a structure-directing agent. The MFI zeolite nanosheet assemblies were composed of MFI nanosheets with randomly organized structure, exhibiting a narrow mesopore distribution. By tuning the Si/Al ratios of MFI zeolite nanosheet assemblies from 60 to 10, the morphology of resultant zeolites changed from nanosheet stacks to house-of-cards-like structures, and to nanosponges. In addition, the porosity and Brønsted acid/Lewis acid ratio exhibited a parabola-type dependence on the Si/Al ratios of obtained zeolites, indicating that meso-/microporosity and acidity of MFI nanosheet assemblies can be systematically tailored by changing the constituents of zeolites. Catalytic performance of MFI zeolite nanosheet assemblies was investigated in the benzylation of benzyl alcohol with mesitylene. The results revealed that MFI zeolite nanosheet assemblies exhibited extraordinary catalytic activity compared to conventional ZSM-5 zeolite. The conversion of benzyl alcohol and selectivity (1,3,5-trimethyl-2-benzylbenzene vs dibenzyl ether) of zeolite catalysts were linearly dependent on the Brønsted acid/Lewis acid ratio, and they exhibited a parabola-type dependence on the S ext /S BET , indicating that a balance between acidity and porosity of zeolites can be realized to modulate the catalytic properties of MFI zeolite nanosheet assemblies guided by C 6-12-diphe .