Promotion effect of niobium on ceria catalyst for selective catalytic reduction of NO with NH3

The CeO 2 , Ce–Nb–O x and Nb 2 O 5 catalysts were synthesized by citric acid method and the promotion effect of Nb on ceria for selective catalytic reduction (SCR) of NO with NH 3 was investigated. The catalytic activity measurements indicate that the mixed oxide Ce–Nb–O x presents a higher SCR activity than the single oxide CeO 2 or Nb 2 O 5 catalyst. In addition, the Ce–Nb–O x catalyst shows high resistance towards H 2 O and SO 2 at 280 °C. The Raman, X-ray photoelectron spectra and temperature programmed reduction with H 2 results indicate that the incorporation of Nb provides abundant oxygen vacancies for capturing more surface adsorbed oxygen, which provides a superior redox capability and accelerates the renewal of active sites. Furthermore, the Fourier transform infrared spectra and temperature programmed desorption of NH 3 results suggest that niobium pentoxide shows high surface acidity, which is partly retained in the Ce–Nb–O x catalyst possessing a high content of Lewis and Brønsted acid sites. Therefore, the incorporation of Nb improves both the redox and acidic capacities of Ce–Nb–O x catalyst for the SCR reaction. Here, the redox behavior is primarily taken on Ce and the acidity is well improved by Nb, so the synergistic effect should exist between Ce and Nb. In terms of the reaction mechanism, in situ DRIFT experiments suggest that both NH 3 on Lewis acid sites and NH 4 + on Brønsted acid sites can react with NO species, and adsorbed NO and NO 2 species can both be reduced by NH 3 . In the SCR process, O 2 primarily acts as the accelerant to improve the redox and acid cycles and plays an important role. This work proves that the combination of redox and acidic properties of different constituents can be feasible for catalyst design to obtain a superior SCR performance. Niobium promotes the redox and acidic capacity of ceria catalyst, showing the synergistic effect of redox and acid cycles for selective catalytic reduction of NO with NH 3 . • Mixed oxide CeNbO x shows a quit higher SCR activity than CeO 2 and Nb 2 O 5 catalyst. • The addition of Nb increases the redox and acidic properties of ceria catalyst. • The redox behavior is primarily taken on Ce and the acidity is well improved by Nb. • The CeNbO x catalyst shows a high resistance towards H 2 O and SO 2 at 280 °C. • Nb mixed ceria shows higher stability than ceria improved by calcining in Ar.