Synthesis and characterization of composite molecular sieves comprising zeolite Beta with MCM-41 structures

Zeolite Beta/MCM-41 composites have been prepared with various crystallinities of zeolite Beta through a two-step crystallization process involving the combination of low crystallinity zeolite Beta synthesis gel with cetyltrimethylammonium bromide surfactant solution. The composites are characterized by XRD, SEM, Si-29 and Al-27 MAS NMR, N-2 adsorption, NH3-TPD and catalytic cracking. The experimental results show that the relative crystallinity of Beta in the composites greatly affects the morphology and surface acidity of the materials, while exhibiting similar Si-29, Al-27 MAS NMR spectra and N-2 adsorption-desorption isotherms. The pore structural data indicate that the composites contain bimodal mesopore systems and microporous structures of zeolite Beta. Although the number of weak acid sites on the composites with various crystallinities of Beta is comparable, composites with higher Beta crystallinity possess more medium acid sites and show higher catalytic activity for n-heptane cracking.