Solvent-Free Synthesis of Mg-Incorporated Nanocrystalline SAPO-34 Zeolites via Natural Clay for Chloromethane-to-Olefin Conversion

Isomorphous substitution is an important approach in modifying the acidity and pore structure of nanoscale SAPO-34 zeolites, which can bring about active sites stemming from heteroatoms. However, it remains a major challenge to use conventional hydrothermal methods to synthesize cost-effective, all-framework heteroatoms, and environmentally friendly catalysts. Herein, an efficient and eco-friendly approach is developed for the solvent-free synthesis of Mg-incorporated SAPO-34 (MgAPSO-34) with Mg content of up to 6.65% and smaller crystal size (50 nm) by taking advantage of a natural layered Mg-rich aluminosilicate clay mineral. Characterizations with X-ray diffraction, magic-angle spinning NMR, and ultraviolet-visible spectroscopies show that all the Mg can enter the zeolitic framework by replacing the Al sites. In addition, MgAPSO-34 with the incorporation of a proper amount of Mg exhibits a high specific surface area and moderate acidity and thus shows excellent performance and anticoke capacity in the chloromethane-to-olefin reaction. The combination of green synthesis and superior catalytic properties allows for low-cost and environmentally friendly synthesis of isomorphous substituted SAPO-34 zeolites with high crystallinity and high quality.