Dual Template Synthesis of Meso- and Microporous MFI Zeolite Nanosheet Assemblies with Tailored Activity in Catalytic Reactions

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Abstract

A dual template synthesis strategy was employed to achieve one-step design of meso- and microporous MFI nanosheet assemblies with tailored morphology, mesoporosity, and catalytic activity. A molecular template (tetrapropylammonium hydroxide, TPAOH) and a polyquaternary ammonium surfactant ([C22H45–N+(CH3)2–C6H12–N+(CH3)2–C6H13]Br2, C22–6–6) were used as cotemplates in the synthesis with a composition of 30Na2O/1Al2O3/100SiO2/10C22–6–6/xTPAOH/4000H2O/18H2SO4. By tuning the concentration of TPAOH (x) from 0 to 20, the morphology of the as-obtained MFI nanosheet assemblies changed from intertwined, to house-of-cards-like, and to dense packing plates. The N2 isotherms showed the hysteresis loop at the range of P/P0 = 0.45–1.0 increases, reaches a maximum, and then decreases with increasing x values, indicating a systematic tailoring of the mesoporosity with TPAOH concentrations. Under strict kinetic control, the rates and apparent activation energies of the ethanol activation in zeolite nanosheet assemblies were comparable. The catalytic conversion of benzyl alcohol in mesitylene showed that the activity of as-obtained MFI zeolites increases, reaching a maximum, and then decreases with increasing x values. The consistency in the variation of morphology, mesoporosity, and catalytic activity with varying x values in the synthesis indicates TPAOH can be used as a secondary template to tailor the textural and catalytic properties of MFI nanosheet assemblies primarily guided by C22–6–6.

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