Engineering SAPO-17/34 Intergrowth Zeolites via Interzeolite Transformation for Enhanced Methanol-to-Olefins Performance

Inspired by the frequent formation of the CHA phase when cyclohexylamine is used as the organic structure-directing agent in SAPO-17 synthesis, we herein propose a simple and efficient interzeolite transformation method for the preparation of SAPO-17/34 intergrowth zeolites using industrial SAPO-34 (CHA topology) as the raw material. During this transformation process, by controlling the crystallization time and adding seed crystals appropriately, the conversion rate from SAPO-34 to SAPO-17 can be effectively adjusted. The study shows that the interzeolite transformation pathway not only promotes the incorporation of more silicon atoms into the SAPO-17 framework but also significantly enhances the specific surface area of the resultant intergrowth zeolite, thereby overcoming the inherent low acidity of conventional SAPO-17. The study also indicates that the conversion from SAPO-34 to SAPO-17 is not a simple direct reconstruction of the double six-membered ring (d6r) but rather a complex, stepwise evolutionary process. Specifically, SAPO-34 first decomposes into nanoparticles, which, under specific conditions, reassemble and grow to eventually form SAPO-17. This finding not only reveals the unique structural evolution mechanism during the interzeolite transformation process but also provides an important theoretical foundation for the performance tuning of zeolite materials. When applied in the methanol-to-olefins (MTO) reaction, this SAPO-17/34 intergrowth zeolite exhibited superior ethylene selectivity and prolonged stability compared with the traditional single-phase SAPO zeolites. These findings establish intergrowth engineering as an effective strategy for developing high-performance zeolite catalysts for the MTO reaction.