Mechanistic study of Ce–La–Fe/γ-Al2O3 catalyst for selective catalytic reduction of NO with NH3

A number of Ce–La–Fe/γ-Al2O3 catalysts were prepared by impregnation and microwave hydrothermal heating based on the ratio of Ce, La, and Fe in natural bastnäsite to examine the synergistic relationship between Ce, La, and Fe in natural bastnäsite and its effects on ammonia selective catalytic reduction (NH3-SCR). The results demonstrated that an increase in Fe species is beneficial to the denitration performance of catalysts with a Ce:La:Fe mole ratio of 1:0.6:0.12, thus providing high NO conversion (>95%) at 350 °C. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy results confirmed the formation of a solid solution between Ce, La, and Fe in the catalysts. The BET isotherms and NH3-TPD demonstrated that the addition of Fe increased the surface area and strengthened the surface acidity of Lewis acid sites. XPS and in situ DRIFTS indicated that electron transfer occurred between Fe3+/Fe2+ and Ce4+/Ce3+ redox cycles in the catalyst, thereby improving the adsorption and activation ability of NO and NH3. NO species were adsorbed on the catalysts in the form of monodentate nitrate, and then monodentate nitrate was oxidized to bidentate nitrate. The SCR reaction route was the coexistence of Eley–Rideal and Langmuir–Hinshelwood mechanisms.