Facet-dependent effect of α-MnO2 on Ag atoms anchoring and low-temperature selective catalytic oxidation of ammonia

Abstract

Ammonia (NH3) contributes greatly to haze formation, posing significant risks to ecology and health. As a typical NH3 selective catalytic oxidation (NH3-SCO) catalyst, Ag supported catalysts can balance activity and selectivity. In this research, Ag atoms were anchored on the various crystal facets ({310}, {110} and {100}) of α-MnO2 and were studied for the NH3-SCO. The facet-dependence on Ag atoms anchoring mechanism, as well as the anchored Ag structure, have all been revealed in detail. It was found that the capturing of Ag on the facets of α-MnO2 followed the terminal hydroxyl anchoring mechanism, and further confirmed the linear relationship between Ag capturing quantity and the amount of terminal hydroxyl groups. The {310} facet has a strong ability to activate water molecules to produce surface hydroxyl groups, thereby exhibiting a heightened capability to capture Ag atoms; Ag atoms are loaded in the form of fine nanoparticles on the {310} facet, while anchored in a highly dispersed form on the {110} and {100} facets. The anchoring of Ag significantly improves the NH3-SCO performance of α-MnO2, especially, the Ag/α-MnO2 catalyst with Ag anchoring on the {310} facets exhibited the best activity, achieving 100 % conversion and greater than 80 % N2 selectivity at as low temperature as 100 °C. Finally, the adsorption and possible NH3-SCO mechanism of Ag/α-MnO2 catalysts were also explored by in-situ DRIFTS. The aim of this research is to reveal the facet-dependence of α-MnO2on Ag atoms anchoring,and its effect on low-temperature NH3-SCO activity.