Effect of SO2 and SO3 Exposure to Cu-CHA on Surface Nitrate and N2O Formation for NH3–SCR

• Published in: ACS Engineering Au Vol. 4; no. 4; pp. 405 - 421
• Main Authors: Han, Joonsoo, Bjerregaard, Joachim D., Grönbeck, Henrik, Creaser, Derek, Olsson, Louise
• Format: Journal Article
• Language: English
• Published: American Chemical Society 21.08.2024
• Subjects: N2O; Cu-CHA; TPD (temperature-programmed desorption); SO2/SO3-exposure; AN (ammonium nitrate)
• ISSN: 2694-2488; 2694-2488
• DOI: 10.1021/acsengineeringau.4c00004

We report effects of SO2 and SO3 exposure on ammonium nitrate (AN) and N2O formation in Cu-CHA used for NH3–SCR. First-principles calculations and several characterizations (ICP, BET, XRD, UV–vis–DRS) were applied to characterize the Cu-CHA material and speciation of sulfur species. The first-principles calculations demonstrate that the SO2 exposure results in both (bi)­sulfite and (bi)­sulfate whereas the SO3 exposure yields only (bi)­sulfate. Furthermore, SOx adsorption on framework-bound dicopper species is shown to be favored with respect to adsorption onto framework-bound monocopper species. Temperature-programmed reduction with H2 shows two clear reduction states and larger sulfur uptake for the SO3-exposed Cu-CHA compared to the SO2-exposed counterpart. Temperature-programmed desorption of formed ammonium nitrate (AN) highlights a significant decrease in nitrate storage due to sulfur species interacting with copper sites in the form of ammonium/copper (bi)­bisulfite/sulfate. Especially, highly stable sulfur species from SO3 exposure influence the NO2–SCR chemistry by decreasing the N2O selectivity during NH3–SCR whereas an increased N2O selectivity was observed for the SO2-exposed Cu-CHA sample. This study provides fundamental insights into how SO2 and SO3 affect the N2O formation during ammonium nitrate decomposition in NH3–SCR applications, which is a very important topic for practical applications.