Improvement of low-temperature NH3-SCR catalytic performance over nitrogen-doped MOx-Cr2O3-La2O3/TiO2-N (M = Cu, Fe, Ce) catalysts

A series of MOx-Cr2O3-La2O3/TiO2-N (M = Cu, Fe, Ce) catalysts with nitrogen doping were prepared via the impregnation method. Comparing the low-temperature NH3-SCR activity of the catalysts, CeCrLa/Ti-N (xCeO(2)-yCr(2)O(3)-zLa(2)O(3)/TiO2-N) exhibited the best catalytic performance (NO conversion approaching 100% at 220-460 degrees C). The physico-chemical properties of the catalysts were characterized by XRD, BET, SEM, XPS, H-2-TPR, NH3-TPD and in situ DRIFTS. From the XRD and SEM results, N doping affects the crystalline growth of anatase TiO2 and MOx (M = Cu, Fe, Ce, Cr, La) which were well dispersed over the support. Moreover, the doping of N promotes the increase of the Cr6+/Cr ratio and Ce3+/Ce ratio, and the surface chemical adsorption oxygen content, which suggested the improvement of the redox properties of the catalyst. And the surface acid content of the catalyst increased with the doping of N, which is related to CeCrLa/TiO2-N having the best catalytic activity at high temperature. Therefore, the CeCrLa/TiO2-N catalyst exhibited the best NH3-SCR performance and the redox performance of the catalysts is the main factor affecting their activity. Furthermore, in situ DRIFTS analysis indicates that Lewis-acid sites are the main adsorption sites for ammonia onto CeCrLa/TiO2-N and the catalyst mainly follows the L-H mechanism.

Automated summary

The CeCrLa/TiO2-N catalyst with nitrogen doping showed the best low-temperature NH3-SCR activity, mainly influenced by its redox properties and surface acidity. Lewis acid sites were identified as the main adsorption sites for ammonia, and the catalyst mainly followed the L-H mechanism.