Temperature-driven dynamic evolution process of Ag species on silver-loaded Zr0.2Sn0.8O2 catalyst for selective catalytic oxidation of ammonia

Abstract

Silver-based catalysts are extensively utilized in the selective catalytic oxidation of ammonia (NH3-SCO). However, enhancing low-temperature activity often causes a decline in N2 selectivity, presenting a substantial challenge in balancing activity and N2 selectivity. In this work, we introduced zirconium into the SnO2 support, resulting in a significant enhancement of low-temperature activity by 200 °C for the Ag/Zr0.2Sn0.8O2 catalyst; yet, this also led to the formation of N2O at low temperatures and NOx at high temperatures. Characterizations such as XPS and in situ DRIFTS revealed that the dynamic changes of silver species driven by temperature had a profound impact on the reaction mechanism and guided the formation of different products. Below 200 °C, the predominance of Ag+ directed the imide mechanism, with the –HNO species being the key intermediate leading to the production of N2O. Above 300 °C, Ag0 became dominant, favoring the internal selective catalytic reduction (i-SCR) mechanism and the production of NOx. This work provides novel insights into improving N2 selectivity of Ag-based catalysts and contributes to a deeper understanding of the reaction mechanisms.