Synergistic effect of niobium and ceria on anatase for low-temperature NH3-SCR of NO process

Abstract A series of TiO2 supported with different contents of Nb (0%, 15%) and Ce (0%, 10%, 15%) active components were prepared by impregnation. 15%Nb2O5–10%CeO2/TiO2 (15Nb10Ce/Ti) catalyst exhibited the best NH3-SCR performance due to an optimum synergistic effect of Nb and Ce. X-ray diffraction, N2 adsorption, X-ray photoelectron spectroscopy (XPS) and Temperature-programmed reduction (TPR) by hydrogen etc. were used to reveal the synergistic effect based on the relationship of acidity, chemisorbed oxygen, Ce3+/Ce4+ content and redox properties with the catalytic performance. Furthermore, the reaction mechanism was studied by using in-situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy to monitor the change of ammonia and NO adsorption species upon temperature. The main ad-NH3 species was NH4+ species at low temperature (150 °C and 200 °C), while amide species at high temperature (300 °C). At low temperature, the monodentate nitrito as the active NO adsorption species reacted with NH4+, which was consistent with the Langmuir–Hinshelwood mechanism. At high temperature, the gas NO reacted with amide (NH2) with the mechanism transformed to Eley–Rideal mechanism.