Assessing Cu2+ active sites evolution on Cu-SSZ-13 NH3-SCR catalysts during hydrothermal aging: A transient response approach

• Published in: Applied catalysis. B, Environmental Environmental, 2024-08, Vol.351, p.123989, Article 123989
• Main Authors: Iacobone, Umberto, Nasello, Nicole Daniela, Nova, Isabella, Tronconi, Enrico, Daya, Rohil, An, Hongmei, Menon, Unmesh
• Format: Article
• Language: English
• Subjects: Cu-CHA catalysts; Cu2+ speciation; Hydrothermal aging; Multinuclear Cu2+ species; NH3-SCR redox mechanism
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2024.123989

Hydrothermal aging (HTA) conditions are commonly reached in Diesel engine NH3-SCR architectures based on Cu-CHA catalysts, altering the catalyst performance due to irreversible transformations of the catalytic sites. Relying on transient response methods (TRMs), we study two Cu-SSZ-13 samples with different HTA extents. The following conclusions apply: i) the Cu2+content is invariant with HTA; ii) the ZCu2+(OH)- population decreases concurrent to the increase of the Z2Cu2+ fraction and to iii) the loss of Brønsted acidity. This evidence agrees with the simple stoichiometry proposed for mild HTA processes: ZCu2+(OH)-+ZH+→Z2Cu2++H2O. Furthermore, TRMs permit to observe additional phenomena which comply with a low-T Cu2+-pair mediated reduction pathway recently proposed. The results from a comprehensive set of simple experimental flow reactor methods consolidate the proposed aging mechanism, strengthen the SCR reduction half cycle (RHC) mechanistic understanding and showcase TRMs as a viable alternative to more complex techniques for the characterization of Cu-CHA catalysts. [Display omitted] •Transient response methods assess hydrothermal aging mechanism and Cu2+ speciation.•The overall reducible Cu2+ fraction from NO+NH3 titration is unaffected by HTA.•ZCu2+(OH)- population measured via NO2-TPD decreases upon hydrothermal aging.•Cu2+ nuclearity in low-T SCR-RHC probed via CO oxidation experiments.