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

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–1 (Δ18O = 24 cm–1) is assigned to a stretching vibration of a thermodynamically favored mono-(μ-oxo) dicoppe...