Hierarchical Beta aggregates assembled from sheet-like nanocrystals: Synthesis and enhanced catalytic application in acylation and alkylation reactions.

The precise control of the self-assembled nano-zeolites is crucial for generating more efficient and stable zeolite-based heterogeneous catalysts, which can considerably promote the development of green catalytic processes. Herein, hierarchical zeolite Beta aggregates assembled from sheet-like nanocrystals were obtained by two-stage varying temperature crystallization of a concentrated gel containing a small amount of polyvinylpyrrolidone (PVP) additives. The introduced PVP could function as growth modifier to modulate the particle size, morphology and porosity of the zeolites. The resultant H-form Beta aggregates with high crystallinity and mesopore volume showed improved catalytic efficiency and lifetime against deactivation for the acylation of anisole with acetic anhydride and for the alkylation of benzene with ethylene. The enhanced catalytic performance could be mainly related to the improvement of accessibility of acid sites and the mass transport ability of Beta aggregates. This work demonstrates that rationally utilizing PVP modifier allows the fine control of the morphology and microstructure of zeolite Beta crystals to meet the sustainable innovation involving zeolite-based solid acid catalysis.