Effect of synthesis conditions on the structural and catalytic properties of hierarchically structured ZSM-5 zeolites

Hierarchically structured ZSM-5 zeolites were synthesized by employing only one dual-porogenic surfactant, and the hydrothermal crystallization of hierarchical structured zeolites were investigated under rotating and static synthesis conditions. X-Ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N-2 adsorption-desorption isotherms, Al-27 magic-angle spinning nuclear magnetic resonance (Al-27 MAS NMR) and thermogravimetric analysis (TGA) were used to characterize the structural and textural features of the resultant zeolite products. By tuning the synthesis conditions from rotating to static, the morphology of the as-obtained hierarchical structure ZSM-5 zeolites changed from silk-like to nanoparticles with a disordered arrangement. Furthermore, the obtained zeolites under static conditions showed a higher BET surface area and lower total pore volume than those of zeolites synthesized under rotating conditions. In addition, quantum chemical calculation results show that the inner ammonium groups may have greater contribution in directing the zeolite structure than tailed ammonium groups. More importantly, the hierarchical structured ZSM-5 zeolites synthesized under static conditions exhibited a higher benzyl alcohol conversion rate and lower ester selectivity compared to those of the samples prepared under rotating conditions. Consideration of the effects of synthesis conditions may be useful for modulating the textural and catalytic properties of hierarchical zeolites.