摘要
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℃.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 Br?nsted 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 Bronsted 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.
基金
Project supported by the Postdoctor Research Foundation of Shunde Graduate School of University of Science and Technology Beijing(2020BH012)
the National Key Research&Development Projects(2021YFC1910504)
the National Natural Science Foundation of China(U2002212)
the Fundamental Research Funds for the Central Universities(FRF-IDRY-20-005)。
