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

The CeO,Ce-Nb-Oand NbOcatalysts were synthesized by citric acid method and the promotion effect of Nb on ceria for selective catalytic reduction(SCR) of NO with NHwas investigated.The catalytic activity measurements indicate that the mixed oxide Ce-Nb-Opresents a higher SCR activity than the single oxide CeOor NbOcatalyst.In addition,the Ce-Nb-Ocatalyst shows high resistance towards HO and SOat 280℃.The Raman,X-ray photoelectron spectra and temperature programmed reduction with Hresults 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 NHresults suggest that niobium pentoxide shows high surface acidity,which is partly retained in the Ce-Nb-Ocatalyst possessing a high content of Lewis and Br?nsted acid sites.Therefore,the incorporation of Nb improves both the redox and acidic capacities of Ce-Nb-Ocatalyst 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 NHon Lewis acid sites and NH~+ on Bronsted acid sites can react with NO species,and adsorbed NO and NOspecies can both be reduced by NH.In the SCR process,Oprimarily 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.