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

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, N-2 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 degrees C and 200 degrees C), while amide species at high temperature (300 degrees 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.