Improvement of low-temperature NH(3)-SCR catalytic performance over nitrogen-doped MO(x)–Cr(2)O(3)–La(2)O(3)/TiO(2)–N (M = Cu, Fe, Ce) catalysts

A series of MO(x)–Cr(2)O(3)–La(2)O(3)/TiO(2)–N (M = Cu, Fe, Ce) catalysts with nitrogen doping were prepared via the impregnation method. Comparing the low-temperature NH(3)-SCR activity of the catalysts, CeCrLa/Ti–N (xCeO(2)–yCr(2)O(3)–zLa(2)O(3)/TiO(2)–N) exhibited the best catalytic performance (NO conversion approaching 100% at 220–460 °C). The physico-chemical properties of the catalysts were characterized by XRD, BET, SEM, XPS, H(2)-TPR, NH(3)-TPD and in situ DRIFTS. From the XRD and SEM results, N doping affects the crystalline growth of anatase TiO(2) and MO(x) (M = Cu, Fe, Ce, Cr, La) which were well dispersed over the support. Moreover, the doping of N promotes the increase of the Cr(6+)/Cr ratio and Ce(3+)/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/TiO(2)–N having the best catalytic activity at high temperature. Therefore, the CeCrLa/TiO(2)–N catalyst exhibited the best NH(3)-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/TiO(2)–N and the catalyst mainly follows the L–H mechanism.