Precursor and dual-template assisted synthesis of highly acidic SAPO-17 molecular sieve: Excellent NH3-SCR activity of Cu-exchanged forms

Silicoaluminophosphate (SAPO) molecular sieves possess diverse architectures and exceptional high-temperature hydrothermal stability, rendering them important acid catalysts. However, enhancing acid concentration of certain SAPO materials remains challenging, which limits their catalytic applications. Here, we report the synthesis of a series of SAPO materials using a developed SAPO precursor plus dual template (SPDT) strategy. A variety of SAPO materials characterized by high silica content and enhanced acidity, such as SAPO-34/56 intergrowths, SAPO-56, and SAPO-17, have been synthesized and thoroughly characterized using various techniques including integrated differential phase-contrast scanning transmission electron microscopy, two-dimensional solid-state nuclear magnetic resonance spectroscopy, and continuous rotation electron diffraction. The use of silica-enriched SAPO precursor combined with the flexible selection of the second template enables the crystalline phase regulation and improves the Si atoms incorporation into the framework. Notably, the synthesized SAPO-17 with abundant Si(4Al) species and unprecedentedly high acid density exhibits exceptional DeNO x activity after Cu loading, with NO x conversion exceeding 90% at 175–700 °C. This outstanding performance can be attributed to the unique ERI structure and the increased acidity of SAPO-17. This work not only presents an effective method for synthesizing SAPO molecular sieves with enhanced acidity but also offers a new perspective for expanding the active temperature range of the ammonia selective catalytic reduction reaction.