A fast organic template-free, ZSM-11 seed-assisted synthesis of ZSM-5 with good performance in methanol-to-olefin

Abstract

This work demonstrated a novel and efficient route for preparing ZSM-5 zeolite by adding ZSM-11 seeds in a template-free system. Compared to conventional ZSM-5-seeded synthesis using crystallization time of 36h, ZSM-11 seeds drove the crystallization of ZSM-5 in much shorter time (12–16h). Particularly, as used hierarchical ZSM-11 seeds with intergrowth morphology, numerous small ZSM-5 crystals with size of 1–2μm could be obtained in a very short period (12h). Both the seed and product zeolites were characterized by XRD, XRF, 27Al MAS NMR, SEM, FTIR and N2 adsorption–desorption analysis. It was found that the existence of terminal Si–OH units on the surface of ZSM-11 seed particles was principally responsible for the fast crystallization of target ZSM-5 zeolites. Moreover, the external surface area provided by the seeds played a vital role in accelerating the nucleation rate by offering specific sites for the formation of nuclei. When applied in the methanol to olefins (MTO) reaction, small ZSM-5 crystals obtained in the hierarchical ZSM-11-seeded system exhibited both a high selectivity to C2=–C4= olefins and a low deactivation rate. In general, this green synthesis route gives enlightenment for designing the synthesis of zeolites with good performance by using seed crystals with special properties.