Hybrid Micrometer Seed-Assisted Synthesis of Submicron Rectangular SAPO-34/18 Intergrowth Zeolites with Enhanced Methanol-to-Olefin Conversion

Efficient synthesis of SAPO-34/18 zeolites with relatively small crystal sizes has hitherto been difficult to achieve without expensive templates, abundant nanosized seeds, or additional crystal growth inhibitors for industrial MTO. Herein, we present a cost-effective and eco-friendly synthetic approach for submicrometer SAPO-34/18 intergrowth zeolites using triethylamine as the template with the assistance of hybrid micrometer seeds. In this work, the micrometer seeds, originally synthesized using triethylamine as the template, were hybridized with a precursor containing dimethylamine under hydrothermal conditions. The resultant SAPO-34/18 intergrowth zeolite exhibits a rectangular morphology and a reduced crystal size of approximately 700 nm. MAS NMR experiments show that as-synthesized SAPO-34/18 intergrowth zeolites with triethylamine as the sole template contained more Si(4Al) and Si(3Al) species. It is found that the d6r units in the hybrid seeds significantly improved nucleation, atom distribution, and etching resistance of SAPO-34/18 products. In addition, the submicrometer SAPO-34/18 intergrowth catalyst exhibited a 3-fold increased catalyst life and improved selectivity (88.3%) for light olefins in the MTO reaction. Therefore, the combination of efficient synthesis and good catalytic performance enables sustainable industrial synthesis of SAPO-34/18 intergrowth zeolites with reduced crystal size.