Chemical Crosslinking Assembly of ZSM-5 Nanozeolites into Uniform and Hierarchically Porous Microparticles for High-Performance Acid Catalysis.

Hierarchically porous zeolites combining the advantages of desirable mass transport of nanozeolites and easy separation and handling of micro-zeolites are ideal candidates in catalytic applications. Facile routes for the assembly of zeolite microparticles with hierarchical porosity and high mechanical strength are much expected. Herein, based on a microfluidic jet spray drying technology, we report a facile and scalable chemical crosslinking assembly strategy for the synthesis of hierarchical zeolite microparticles by directly using the conventional as-synthesized nanozeolite suspension as a precursor. This route not only avoids the energy-intensive centrifugal separation process of nanozeolites but also significantly increases the uniformity and mechanical strength of the microparticles. The soluble aluminosilicate species act as a stabilizer to improve the droplet stability during the drying process and then as a "cross-linker" to chemically bind and interconnect zeolite nanoparticles to form robust bodies after drying and calcination. Zeolite microparticles with variable morphologies (spherical, bowl-like, and dimpled) and uniform and controllable sizes (from 70 to 108 μm) can be obtained by adjusting the experimental parameters. The particle formation mechanism is discussed based on the zeolite microparticles obtained from the purified nanozeolite suspension as a control. The zeolite microparticles possess emerged uniform mesopores (∼6 nm) and a well-maintained high surface area, large pore volume, high microporosity, and strong acidity of the original nanozeolites. As a result, they exhibit excellent acid catalytic performances in acetolysis of epichlorohydrin and catalytic cracking of low-density polyethylene, far better than those of the commercial ZSM-5.