Formation of [Cu2O2]2+ and [Cu2O]2+ toward C-H Bond Activation in Cu-SSZ-13 and Cu-SSZ-39

Bahar Ipek, Matthew J. Wulfers, Hacksung Kim, Florian Göltl, Ive Hermans, Joseph P. Smith, Karl S. Booksh, Craig M. Brown, Raul F. Lobo*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

87 Scopus citations

Abstract

Cu-exchanged small-pore zeolites (CHA and AEI) form methanol from methane (>95% selectivity) using a 3-step cyclic procedure (Wulfers et al. Chem. Commun. 2015, 51, 4447-4450) with methanol amounts higher than Cu-ZSM-5 and Cu-mordenite on a per gram and per Cu basis. Here, the CuxOy species formed on Cu-SSZ-13 and Cu-SSZ-39 following O2 or He activation at 450°C are identified as trans-μ-1,2-peroxo dicopper(II) ([Cu2O2]2+) and mono-(μ-oxo) dicopper(II) ([Cu2O]2+) using synchrotron X-ray diffraction, in situ UV-vis, and Raman spectroscopy and theory. [Cu2O2]2+ and [Cu2O]2+ formed on Cu-SSZ-13 showed ligand-to-metal charge transfer (LMCT) energies between 22,200 and 35,000 cm-1, Cu-O vibrations at 360, 510, 580, and 617 cm-1 and an O-O vibration at 837 cm-1. The vibrations at 360, 510, 580, and 837 cm-1 are assigned to the trans-μ-1,2-peroxo dicopper(II) species, whereas the Cu-O vibration at 617 cm-118O = 24 cm-1) is assigned to a stretching vibration of a thermodynamically favored mono-(μ-oxo) dicopper(II) with a Cu-O-Cu angle of 95°. On the basis of the intensity loss of the broad LMCT band between 22,200 and 35,000 cm-1 and Raman intensity loss at 571 cm-1 upon reaction, both the trans-μ-1,2-peroxo dicopper(II) and mono-(μ-oxo) dicopper(II) species are suggested to take part in methane activation at 200°C with the trans-μ-1,2-peroxo dicopper(II) core playing a dominant role. A relationship between the [Cu2Oy]2+ concentration and Cu(II) at the eight-membered ring is observed and related to the concentration of [CuOH]+ suggested as an intermediate in [Cu2Oy]2+ formation. (Chemical Equation Presented).

Original languageEnglish (US)
Pages (from-to)4291-4303
Number of pages13
JournalACS Catalysis
Volume7
Issue number7
DOIs
StatePublished - Jul 7 2017

Keywords

  • Cu-SSZ-13
  • Cu-SSZ-39
  • Cu-zeolite
  • Raman spectroscopy
  • active site
  • dicopper core
  • methane activation

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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