The role of silver species on Ag/Al2O3 catalysts for the selective catalytic oxidation of ammonia to nitrogen

The role of Ag species on Ag/Al2O3 catalyst for the selective catalytic oxidation (SCO) of NH3 to N2 was studied using 10 wt% Ag/Al2O3 catalysts prepared with impregnation, incipient wetness impregnation and sol–gel methods. The catalyst characterization was preformed using N2 adsorption–desorption, UV/Vis, TEM and XRD. O2-chemisorption and H2–O2 titration were measured to confirm the metal dispersion on the catalyst. The Ag species state and Ag particle size have significant influence on the Ag/Al2O3 activity and N2 selectivity of the SCO of NH3 at low temperature. Ag0 is proposed to be an active species on the H2 pretreated catalyst at low temperature (<140 °C). It is evident that well-dispersed and small particle Ag0 enhances catalytic activity at low temperature, whereas large particle Ag0 is relate to a high N2 selectivity. In contrast, Ag+ could also be the active species at temperatures above 140 °C.