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

Published

July 7, 2017

Author(s)

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

Abstract

Cu- exchanged small-pore zeolites (CHA and AEI) form methanol from methane (>95% selectivity) using a 3-step cyclic procedure (Wulfers, M. J.; Teketel, S.; Ipek, B.; Lobo, R. F. 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 Cu_xO_y species formed on Cu-SSZ-13 and Cu-SSZ-39 following O₂ or He activation at 450 °C are identified as trans-υ1,2-peroxo dicopper(II) and mono–(υ–oxo) dicopper(II) 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 cm^-1 and 35,000 cm^-1, Cu–O vibrations at 360 cm^-1, 510 cm^-1, 580 cm^-1, 617 cm^-1 and an O–O vibration at 837 cm^-1. The vibrations at 360 cm^-1, 510 cm^-1, 580 cm^-1 and 837 cm^-1 are assigned to the trans-υ-1,2-peroxo dicopper(II) species, whereas the Cu–O vibration at 617 cm^-1 (Δ}¹⁸18O = 24 cm^-1) is assigned to a stretching vibration of a thermodynamically favored mono–(υ–oxo) dicopper( II) with an Cu–O–Cu angle of 95 °. Based on the loss of intensity of the broad LMCT band between 22,200 cm^-1 and 35,000 cm^-1 upon reaction, both the trans-υ-1,2-peroxo dicopper(II) and mono–(υ–oxo) dicopper(II) species are suggested to take part in methane activation at 200 °C. A relationship between the [Cu₂O_y]²⁺ concentration and Cu(II) at the eight-membered ring (8MR) is observed and related to the concentration of the [CuOH]⁺, suggested as an intermediate in [Cu₂O_y]²⁺ formation.

Citation

ACS Catalysis

Volume

7

Issue

7

Pub Type

Journals

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Keywords

zeolite, methanol, catalysis, crystallography, structure

Citation

Ipek, B. , Wulfers, M. , Kim, H. , Goeltl, F. , Hermans, I. , Smith, J. , Booksh, K. , Brown, C. and Lobo, R. (2017), Formation of [Cu₂O₂]²⁺ and [Cu₂O]²⁺ Toward C-H Bond Activation in Cu-SSZ-13 and Cu-SSZ-39, ACS Catalysis, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=922229 (Accessed December 21, 2024)