Hierarchical zeolites with high hydrothermal stability prepared via desilication of OSDA-occluded zeolites

Zeolites have been served as multifunctional microporous materials. However, diffusion limitation often exists within zeolitic micropores, limiting their performances. Hierarchical zeolites with meso- or macropores have been synthesized by an effective approach to solving the above problem. Herein, we synthesized hierarchical zeolites via an alkaline treatment for organic structure-directing agents (OSDA)-occluded zeolites. In this method, desilication occurred only on the external surfaces of zeolites thanks to the presence of OSDA, leading to selective formation of mesopores only on the external surfaces of zeolites. The zeolite with mesopores only on external surfaces showed much higher catalytic activity on cracking of low-density polyethylene than a pristine zeolite. The catalytic performance was the same as a conventional hierarchical zeolite with mesopores in overall particles. These results demonstrated that mesopores on the external surfaces of zeolites played important roles in improving mass transfers of the reactants. In addition, the zeolites with mesopores only on the external surfaces showed higher hydrothermal stability than the conventional hierarchical zeolite due to its fewer defects consisting of SiOH or AlOH. This work presented a new strategy for controlling the pore structures of zeolites.