Synergistic oxidation of NH3 and Hg0 over Cu-ATP catalyst: Influence of SO2 and reaction mechanisms

Abstract

NH3 and Hg0 could be synergistically oxidized by copper modified attapulgite (Cu3-ATP) catalyst at the gas hourly space velocity (GHSV) below 5 × 104 h−1 despite competition exist between these two reactions. Its Hg0 oxidation showed good sulfur resistance when HCl was present, but the NH3 oxidation was partially inhibited after SO2 was added. In order to explain this phenomenon, the composition and physical characteristics of Cu3-ATP before and after sulfurization were characterized by XRF, BET, XRD and FTIR. And H2-TPR, NH3-TPD, in situ DRIFT and XPS of the catalysts were adopted to reveal the influence of SO2 on NH3/Hg0 oxidation and the reaction mechanisms. The results showed that SO2 would adsorb and oxidize on the catalyst surface to form very small amount of sulfite and sulfate species, and partially change the composition and structure of Cu3-ATP. This reduced the reducibility of Cu3-ATP and increased the weak and moderate acid sites on its surface. The presence of SO2 was beneficial to NH3 adsorption, but inhibited NH2 → NOx conversion in iSCR mechanism for NH3 oxidation. Cl2 formation were also inhibited by SO2, while the generated surface active Cl and O species could ensure high Hg0 oxidation efficiency.