Importantly, the yields of CH3OH (per mol of Cu) increase monotonically from 0 to ~10 ks over Cu-CHA-I (Figure ), and kapp values measured via Raman (0.31 ks -1 ) and PMO (0.37 ks -1 ) are in close agreement, suggesting that the features within these Raman spectra reflect PMO-relevant active sites proposed previously to be binuclear Cu-oxo site types that require longer timescales to form. A nonnegligible amount of methanol forms on Cu-CHA-I following a pretreatment in helium (Figure ; zero O2 activation time) followed by exposure to methane. The formation of methanol without an intentional oxidative treatment was also observed by Pappas et al. on Cu-CHA and ascribed to a small fraction of Cu remaining as Cu(II) in multinuclear CuxOy structures that do not auto-reduce and are thus able to activate methane. Brezicki et al. reported similar findings for Cu-MOR and instead attributed this to trace oxygen impurities in the sample or reaction apparatus. We cannot exclude the possibility that minority CuxOy species are present that do not auto-reduce and subsequently activate methane, or the possibility of trace oxygen impurities as the reason for non-zero methanol yields observed without intentional oxidative treatments. We can, however, definitively conclude that methanol yields increase with longer O2 activation times (>2 h) due to the formation of the CuxOy structure probed via Raman spectroscopy.