SSZ-16 zeolite with AFX topology was synthesized by hydrothermal method using 1,4-diazabicyclo[2.2.2]-octane-C4-diquat dibromide as organic structure directing agent. Cu x -SSZ-16 catalysts were prepared by exchanging SSZ-16 zeolite with Cu and applied for selective catalytic reduction (SCR) of NO x with ammonia. Among these catalysts, Cu 2.2 -SSZ-16 performs the best SCR denitration (deNO x ) performance that above 90% NO x conversion can be achieved at 175–600 °C. Especially, the influences of the hydrothermal aging at various temperatures (650, 750 and 850 °C) on active species and AFX framework of the Cu 2.2 -SSZ-16 catalyst are investigated in detail by various characterization methods including XRD, SEM , H 2 -TPR, NMR, UV–vis-DRS, EPR, NH 3 -TPD and in situ DRIFTS . Cu 2.2 -SSZ-16 still shows good NH 3 -SCR activity after hydrothermal aging at 650 and 750 °C due to more Cu 2+ -2Z species in the sample. Still, obvious deactivation can be observed after hydrothermal aging at 850 °C because of the collapse of AFX skeleton and the weak interaction between active Cu species and the skeleton. Nevertheless, Cu 2.2 -SSZ-16 is a competitive candidate for NH 3 -SCR deNO x reaction in practical applications.
Ye Wang,Pan Gao,Dan Zhao,Tongrui Liu,Sitong Zhou,Miao Yang,Shiping Liu,Bing Li,Yida Zhou,Wenhao Cui,Guangjin Hou,Peng Tian,Zhongmin Liu
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.
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