Hierarchical SAPO-34 Preparation Based on the Crystal Metastability in Mother Liquor Solution

Fabrication of hierarchical porosity in microporous zeolites is a key to overcoming the inherent mass-transfer limitation and to improving the molecular accessibility to the active sites. The present study reports a facile and cost-effective etching strategy based on crystal metastability to construct a hierarchical SAPO-34 (CHA-type) zeolite. The hierarchical SAPO-34 with high crystallinity is obtained conveniently via an extended hydrothermal treatment without using any additional chemicals. The crystal etching is triggered by the metastability of SAPO-34 in the mother liquor. The hierarchical characteristics of etched SAPO-34 are found dependent on the crystallization-dissolution process controlled by the synthesis temperature and time. The products are systematically investigated by complementary characterization methods providing information on the textural properties and chemical environments of framework atoms. The resultant hierarchical zeolites exhibit improved diffusion and accessibility to the active sites in the micropores. Consequentially, the hierarchical SAPO-34 zeolite shows remarkably enhanced catalytic performance in the methanol-to-olefin (MTO) reaction, compared with its microporous counterpart. The present approach to hierarchical zeolites can be extended to tailor the properties of other zeo-types.