Remarkable N2-selectivity enhancement of practical NH3-SCR over Co0.5Mn1Fe0.25Al0.75Ox-LDO: The role of Co investigated by transient kinetic and DFT mechanistic studies

• Published in: Applied catalysis. B, Environmental Vol. 277; p. 119186
• Main Authors: Chen, Sining, Vasiliades, Michalis A., Yan, Qinghua, Yang, Guangpeng, Du, Xuesen, Zhang, Cheng, Li, Yuran, Zhu, Tingyu, Wang, Qiang, Efstathiou, Angelos M.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15-11-2020; Elsevier BV
• Subjects: Acidity; Ammonia; Carbon dioxide; Catalysts; Co-based NH3-SCR; Cobalt; Density functional theory; Electron transfer; LDHs; Low temperature; MnOx-based catalyst; NH3-SCR; Nitrous oxide; Selectivity; Sulfur dioxide; Switches; Transient kinetics; X ray photoelectron spectroscopy; LDHs; NH3-SCR; MnOx-based catalyst; Co-based NH3-SCR; Transient kinetics
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2020.119186

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•Co0.5Mn1Fe0.25Al0.75Ox-LDO showed remarkable N2-selectivity enhancement.•Use of Co reduced significantly NH3 oxidation to N2O.•Electron transfer between Co3+/Co2+ and Mn4+/Mn3+ suppressed N2O formation.•Transient NH3-SCR clarified the role of Co in improving N2-selectivity.•Transient NH3-SCR strongly suggested L-H mechanism on CoMnFeAlOx-LDO at 250 °C.
A Co0.5Mn1Fe0.25Al0.75Ox-LDO catalyst was developed which showed excellent performance for the low-temperature NH3-SCR. NOx conversions ∼100% were achieved in the whole 100-250 °C range, while after 10-h operation at 150 °C with 100 ppm SO2/5 vol% H2O in the feed, the NOx conversion was maintained at 80%. This catalyst provided a much better N2-selectivity than the Mn1Fe0.25Al0.75Ox-LDO and Mn1Al1Ox-LDO, especially at 150-300 °C. It was found that Co0.5Mn1Fe0.25Al0.75Ox possessed higher surface acidity and reducibility, while XPS analyses indicated an electron transfer between Co3+/Co2+ and Mn4+/Mn3+ redox cycles, leading to a much lower N2O formation, supported by Density Functional Theory (DFT) calculations. Detailed analysis of gas responses obtained upon various step-gas switches was performed, which allowed to measure the surface concentration and reactivity of preadsorbed NOx-s and NHx-s leading to N2 and N2O. Transient kinetic and DFT studies strongly suggested likely mechanisms of NH3-SCR and the critical role of Co for N2-selectivity enhancement.