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Combining the redox properties of Co and the acid properties of Nb in a Co3-Nb-Ox catalyst is shown to provide superior performance in the selective catalytic reduction of NO with NH3 (NH3-SCR).Co3O4 shows average activity,however,it exhibits a poor N2 selectivity.Nb2O5 is not active for NH3-SCR.However,the mixed Co3-Nb-Ox catalyst shows higher NO conversion and N2 selectivity than the single Co3O4 and Nb2O5 catalysts at 100-300 ℃.The results of temperature programmed reduction by H2 and X-ray photoelectron (XP) spectra indicate that the addition of Nb changes the chemical states of Co and decreases the concentration of Co3+ and Oα,adjusting the activity for catalytic oxidation to a moderate level.This suppresses the formation of undesired N2O from the over-oxidation of NH3.Incorporation of Co and Nb into one solid synergistically couples their redox behavior and surface acidity,ensuring the high catalytic activity and N2 selectivity in NH3-SCR.