Evolution of Structure and Active Sites during the Synthesis of ZSM-5: From Amorphous to Fully Grown Structure

Abstract

Lately, to considerably reduce the diffusion constraints in the catalysis performed by zeolites, there has been significant interest in syntheses of partially formed zeolites with extremely accessible active sites, named embryonic zeolites. Their preparation relies on stopping the crystallization of conventional micron-sized zeolites before the zeolites reach full crystallization, as detected by X-ray diffraction. In this current study, ZSM-5 zeolites were synthesized by using the same starting batch without organic template and different times, obtaining amorphous, ill-crystalized, and fully-grown structures that were characterized by various physicochemical methods and used in two catalytic test reactions. Using this synthesis strategy, two significant features of zeolites in catalysis are highlighted: (1) the accessibility of their inner pores for reactants and (2) the confinement effect, the ability of zeolites to stabilize transition states in some catalytic reactions. As the ZSM-5 was being formed, ...