Rare earth ions (La, Nd, Sm, Gd, and Tm) regulate the catalytic performance of CeO₂/Al₂O₃ for NH₃-SCR of NO

A series CeO₂/Al₂O₃ catalysts was modified with rare earth element (La, Nd, Sm, Gd, and Tm) using extrusion method. The catalytic activities of the obtained catalysts were measured for the selective catalytic reduction (SCR) of NO with NH3 to screen suitable addition of rare earth element. These samples were characterized by X-ray diffraction (XRD), N2 adsorption (N2-BET), NH3 temperature-programmed desorption analyses (NH3-TPD), H2 temperature-programmed reduction (H2-TPR), Raman spectra, pyridine adsorption Fourier-transform infrared (Py-IR) and X-ray photoelectron spectroscopy (XPS), respectively. Results showed that the CeO₂/Al₂O₃ exhibited excellent performance in resisting reactant poisoning caused by vapor and sulfur and the highest catalytic activity (98.35%) at 360 °C when the added Tm/Ce molar ratio is 0.10. The surface acidity of CeO₂/Al₂O₃ catalyst would be enhanced with the addition of rare earth ions. Consequently, rare earth ion was beneficial to catalytic activity at low temperatures and corresponded to similar law. Analysis revealed that the higher number of acid sites and the more Ce³⁺ were conductive to obtain the excellent NH3-SCR activity.