The promoting mechanism of in situ Zr doping on the hydrothermal stability of Fe-SSZ-13 catalyst for NH3-SCR reaction

Abstract

Fe-SSZ-13 has been proven to be a highly efficient catalyst for the ammonia selective catalytic reduction (NH3-SCR) of NOx, especially at medium and high reaction temperatures. Nevertheless, the hydrothermal stability of Fe-SSZ-13 catalyst is inferior, limiting its application in vehicle exhaust purification. Impressively, it is found that the hydrothermal stability of Fe-SSZ-13 can be remarkably enhanced (as high as 30 % improvement at 300 °C) by in situ introduction of Zr and Fe into initial gels via one-pot synthesis in this work. A small amount of Zr addition (0.31 wt.%) is beneficial for improving the relative crystallinity of Fe-SSZ-13. The characterization results (obtained by 27Al NMR, NH3-TPD, UV–vis, XPS and in situ DRIFTS) revealed that Zr doping by a one-pot method would not only enhance the dispersion of active isolated Fe ions but also inhibit the migration and agglomeration of isolated Fe ions during hydrothermal aging, improving the stability of the catalyst. Additionally, the introduction of Zr generates new hydroxy groups and Lewis acid sites, facilitating the formation of reaction intermediates, such as -NH2, -HNO2, -NO2, etc., and promoting the SCR reaction especially over the aged catalyst.