Synergistic effect of cobalt and niobium in Co3-Nb-Ox on performance of selective catalytic reduction of NO with NH3

Combining the redox properties of Co and the acid properties of Nb in a Co 3 -Nb-O x catalyst is shown to provide superior performance in the selective catalytic reduction of NO with NH 3 (NH 3 -SCR). Co 3 O 4 shows average activity, however, it exhibits a poor N 2 selectivity. Nb 2 O 5 is not active for NH 3 -SCR. However, the mixed Co 3 -Nb-O x catalyst shows higher NO conversion and N 2 selectivity than the single Co 3 O 4 and Nb 2 O 5 catalysts at 100–300 °C. The results of temperature programmed reduction by H 2 and X-ray photoelectron (XP) spectra indicate that the addition of Nb changes the chemical states of Co and decreases the concentration of Co 3+ and O α , adjusting the activity for catalytic oxidation to a moderate level. This suppresses the formation of undesired N 2 O from the over-oxidation of NH 3 . Incorporation of Co and Nb into one solid synergistically couples their redox behavior and surface acidity, ensuring the high catalytic activity and N 2 selectivity in NH 3 -SCR. Graphical Abstract