Enhanced selectivity to benzaldehyde in the liquid phase oxidation of benzyl alcohol using nanocrystalline ZSM-5 zeolite catalyst

摘要

In the present paper, nanocrystalline hierarchical ZSM-5 zeolites were successfully synthesized by the hydrothermal method in the presence of tetrapropylam-monium hydroxide as a single template with the gel composition of 58SiO_2:Al_2O_3:20TPAOH:1,500H_2O. The prepared zeolite catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Nitrogen adsorption-desorption (BET), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM) techniques. The formation of pure and highly crystalline ZSM-5 zeolite phase is confirmed by XRD. The IR vibration band at 550 cm~(-1) is assigned to the double 5-rings of MFI-type zeolites. N_2 adsorption-desorption isotherms showed that the synthesized product had high BET surface area and possessed composite pore structures with both micro and mesopores. The catalytic performance of hierarchical ZSM-5 zeolite was investigated in the selective oxidation of benzyl alcohol (BzOH) with hydrogen peroxide (H_2O_2) under mild conditions. The results showed that the conversion of BzOH and the selectivity to benzaldehyde were about 94 and about 99 % respectively, when using 0.08 g ZSM-5 catalyst with acetonitrile as the solvent and H_2O_2 as the oxidant at 90 ℃. This catalyst can be retrieved and reprocessed for five times without a significant loss in its activity and selectivity.