The role of silver species on Ag/Al 2O 3 catalysts for the selective catalytic oxidation of ammonia to nitrogen

Abstract

The role of Ag species on Ag/Al 2O 3 catalyst for the selective catalytic oxidation (SCO) of NH 3 to N 2 was studied using 10 wt% Ag/Al 2O 3 catalysts prepared with impregnation, incipient wetness impregnation and sol–gel methods. The catalyst characterization was preformed using N 2 adsorption–desorption, UV/Vis, TEM and XRD. O 2-chemisorption and H 2–O 2 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/Al 2O 3 activity and N 2 selectivity of the SCO of NH 3 at low temperature. Ag 0 is proposed to be an active species on the H 2 pretreated catalyst at low temperature (<140 °C). It is evident that well-dispersed and small particle Ag 0 enhances catalytic activity at low temperature, whereas large particle Ag 0 is relate to a high N 2 selectivity. In contrast, Ag + could also be the active species at temperatures above 140 °C.