Effect of SO 2 and SO 3 Exposure to Cu-CHA on Surface Nitrate and N 2 O Formation for NH 3 –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: United States 21.08.2024
• Subjects: AN (ammonium nitrate); Cu-CHA; N2O; SO2/SO3-exposure; TPD (temperature-programmed desorption)
• ISSN: 2694-2488; 2694-2488
• DOI: 10.1021/acsengineeringau.4c00004

We report effects of SO and SO exposure on ammonium nitrate (AN) and N O formation in Cu-CHA used for NH -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 SO exposure results in both (bi)sulfite and (bi)sulfate whereas the SO 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 H shows two clear reduction states and larger sulfur uptake for the SO -exposed Cu-CHA compared to the SO -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 SO exposure influence the NO -SCR chemistry by decreasing the N O selectivity during NH -SCR whereas an increased N O selectivity was observed for the SO -exposed Cu-CHA sample. This study provides fundamental insights into how SO and SO affect the N O formation during ammonium nitrate decomposition in NH -SCR applications, which is a very important topic for practical applications.