title: Isolation of the copper redox steps in the standard selective catalytic reduction on Cu-SSZ-13.
abstract: Operando X-ray absorption experiments and density functional theory (DFT) calculations are reported that elucidate the role of copper redox chemistry in the selective catalytic reduction (SCR) of NO over Cu-exchanged SSZ-13. Catalysts prepared to contain only isolated, exchanged Cu(II) ions evidence both Cu(II) and Cu(I) ions under standard SCR conditions at 473 K. Reactant cutoff experiments show that NO and NH3 together are necessary for Cu(II) reduction to Cu(I). DFT calculations show that NO-assisted NH3 dissociation is both energetically favorable and accounts for the observed Cu(II) reduction. The calculations predict in situ generation of Brønsted sites proximal to Cu(I) upon reduction, which we quantify in separate titration experiments. Both NO and O2 are necessary for oxidation of Cu(I) to Cu(II), which DFT suggests to occur by a NO2 intermediate. Reaction of Cu-bound NO2 with proximal NH4(+) completes the catalytic cycle. N2 is produced in both reduction and oxidation half-cycles.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Notre Dame, 182 Fitzpatrick Hall, Notre Dame, IN 46556 (USA).
authors.forename: Christopher
authors.initials: C
authors.lastname: Paolucci
authors.forename: Anuj A
authors.initials: AA
authors.lastname: Verma
authors.forename: Shane A
authors.initials: SA
authors.lastname: Bates
authors.forename: Vincent F
authors.initials: VF
authors.lastname: Kispersky
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Miller
authors.forename: Rajamani
authors.initials: R
authors.lastname: Gounder
authors.forename: W Nicholas
authors.initials: WN
authors.lastname: Delgass
authors.forename: Fabio H
authors.initials: FH
authors.lastname: Ribeiro
authors.forename: William F
authors.initials: WF
authors.lastname: Schneider
keywords: density functional calculations; heterogeneous catalysis; nitrogen oxides; operando spectroscopy; zeolites