title: The Cu-CHA deNOx Catalyst in Action: Temperature-Dependent NH3-Assisted Selective Catalytic Reduction Monitored by Operando XAS and XES.
abstract: The small-pore Cu-CHA zeolite is today the object of intensive research efforts to rationalize its outstanding performance in the NH3-assisted selective catalytic reduction (SCR) of harmful nitrogen oxides and to unveil the SCR mechanism. Herein we exploit operando X-ray spectroscopies to monitor the Cu-CHA catalyst in action during NH3-SCR in the 150-400 °C range, targeting Cu oxidation state, mobility, and preferential N or O ligation as a function of reaction temperature. By combining operando XANES, EXAFS, and vtc-XES, we unambiguously identify two distinct regimes for the atomic-scale behavior of Cu active-sites. Low-temperature SCR, up to ∼200 °C, is characterized by balanced populations of Cu(I)/Cu(II) sites and dominated by mobile NH3-solvated Cu-species. From 250 °C upward, in correspondence to the steep increase in catalytic activity, the largely dominant Cu-species are framework-coordinated Cu(II) sites, likely representing the active sites for high-temperature SCR.
authors.affiliation: Department of Chemistry, NIS Centre and INSTM Reference Center, University of Turin , via P. Giuria 7, 10125 Turin, Italy.|IRC "Smart Materials", Southern Federal University , Zorge Street 5, 344090 Rostov-on-Don, Russia.
authors.forename: Kirill A
authors.initials: KA
authors.lastname: Lomachenko
authors.affiliation: Department of Chemistry, NIS Centre and INSTM Reference Center, University of Turin , via P. Giuria 7, 10125 Turin, Italy.
authors.forename: Elisa
authors.initials: E
authors.lastname: Borfecchia
authors.affiliation: Department of Chemistry, NIS Centre and INSTM Reference Center, University of Turin , via P. Giuria 7, 10125 Turin, Italy.
authors.forename: Chiara
authors.initials: C
authors.lastname: Negri
authors.affiliation: Department of Chemistry, NIS Centre and INSTM Reference Center, University of Turin , via P. Giuria 7, 10125 Turin, Italy.
authors.forename: Gloria
authors.initials: G
authors.lastname: Berlier
authors.affiliation: Department of Chemistry, NIS Centre and INSTM Reference Center, University of Turin , via P. Giuria 7, 10125 Turin, Italy.|IRC "Smart Materials", Southern Federal University , Zorge Street 5, 344090 Rostov-on-Don, Russia.
authors.forename: Carlo
authors.initials: C
authors.lastname: Lamberti
authors.affiliation: Haldor Topsøe A/S , Haldor Topsøes Allé 1, 2800 Kgs. Lyngby, Denmark.
authors.forename: Pablo
authors.initials: P
authors.lastname: Beato
authors.affiliation: Haldor Topsøe A/S , Haldor Topsøes Allé 1, 2800 Kgs. Lyngby, Denmark.
authors.forename: Hanne
authors.initials: H
authors.lastname: Falsig
authors.affiliation: Department of Chemistry, NIS Centre and INSTM Reference Center, University of Turin , via P. Giuria 7, 10125 Turin, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Bordiga