Rapid hydrothermal synthesis of hierarchical ZSM-5/beta composite zeolites

Abstract

An innovative hydrothermal method has been successfully applied to the synthesis of hierarchical ZSM-5/beta composite zeolites with different mass ratios. Firstly, the ZSM-5 zeolites were coated with amorphous silica and aluminum species by a spray drying process. Then, the precursor powder was hydrothermally crystallized for only 1–2 days with the addition of tetraethyl ammonium hydroxide (TEAOH). The obtained products were characterized by XRD, SEM, TEM, N₂ physical adsorption–desorption, ²⁷Al MAS NMR, ICP, pyridine-IR and NH₃-TPD techniques. The characterization results imply that the ZSM-5/beta composite zeolites exhibit hierarchical-pores, higher external surface areas and larger mesopore volumes as compared to those of the pure ZSM-5 and beta zeolite. Moreover, the pore structure and acid sites of the ZSM-5/beta composite can be adjusted by changing the mass ratio of ZSM-5/beta. Finally, the ZSM-5/beta composite catalysts exhibit good catalytic performances in the cracking of 1,3,5-triisopropylbenzene (1,3,5-TIPB).