BEA nanosponge/ultra-thin lamellar MFI prepared in one-step: Integration of 3D and 2D zeolites into a composite for efficient alkylation reactions

Abstract

The synthesis of hierarchical meso-/microporous zeolite materials with spatially controlled morphology, meso-/microporosity, and acidity is an expanding area of research interest for a wide range of applications. Here, we report a one-step dual template synthesis method for integration of 3-dimensional (3D) BEA nanosponge and ultra-thin 2D lamellar MFI into a new type of hierarchical meso-/microporous zeolite composite structures. Specifically, the 2D layered MFI nanosheets were laid over the surface of or interdigitated into the 3D BEA particles in the bulk BEA nanosponge-lamellar MFI (BBLM) zeolite structure, which generated a unique morphology of interconnected micropores and mesopores underneath the "skinning" shell (~3-10 nm) of MFI nanosheets. The BBLM zeolites have higher mesoporosity than either bare BEA or lamellar MFI zeolites. The micropore size decreases with increasing lamellar MFI component in the composite. The fraction of external acid sites of BBLM zeolite composite, represented by the percentage of active sites accessible to bulky organic base molecules, decreases with increasing MFI component. Additionally, the types of acid sites are diversified in the BBLM composites compared to either bare BEA or lamellar MFI zeolites. The catalysis tests using conversion of benzyl alcohol in mesitylene showed that BBLM zeolites had significant higher activity and durability than single zeolites or their physical mixture. The BBLM composite zeolite provides a good model catalyst with integrated 2D-3D structures and meso-/microporosity for studying a series of important catalytic reactions in hierarchical zeolites. The one-step dual template synthesis method described herein is versatile and facile, which may prove to be a general platform for hierarchical composite zeolite design at the unit-cell scales of zeolites and with potentially broader applicability to other porous materials.

Synthesis of Engineered Zeolitic Materials: From Classical Zeolites to Hierarchical Core–Shell Materials

“…In his recent review, Schwieger has assigned the hierarchy within these examples as compositional, but not transport‐related . Although the presence of a mesoporous zeolite shell may provide a real hierarchy to the system, as well as plenty of beneficial synergetic effects, it should be remembered that one of the main reasons for using core@shell materials is their shape‐selective property which is guaranteed by having an entirely microporous zeolitic shell.…”

“…For instance, bulk ZSM‐5 microcrystals covered with a hierarchical ZSM‐5 shell, e.g., vesicular or lamellar ZSM‐5 zeolite shells, were synthesized from a homogeneous zeolite gel mixture using a dual‐templating technique . Recently, Emdadi et al have established a one‐step dual template synthesis technique to synthesize core@shell zeolitic particles with hierarchical mesoporous/microporous composite structures using two structure‐directing agents . This report was the first example of a zeolite@zeolite material with two structurally different zeolites (BEA@MFI).…”