The Cu-CHA samples studied here will be referred to as Cu-CHA-I, Cu-CHA-P or Cu-CHA-M where I, P, and M contain Cu exchanged at predominantly 6-MR isolated Al sites, 6-MR paired Al sites, or mixtures thereof, respectively. All Cu-CHA samples exhibit UV-Vis absorption features between 8,000 and 20,000 cm -1 after O2 activation at 723 K (Figures ), which are consistent with the Cu speciation expected within Cu-CHA materials that contain predominantly ZCuOH sites, Z2Cu, or mixtures thereof. Figure shows in situ resonance Raman spectra of Cu-CHA-I during O2 activation, demonstrating that more than 7 ks (~2 h) at 723 K is required for CuxOy to reach their steady-state structures. These spectra were obtained with an excitation wavelength of 532 nm to achieve resonance Raman spectra. To capture the transient changes in the number of Raman-active species, we continuously collect Raman spectra during O2 activation. Multivariate curve resolution-alternating least squares (MCR-ALS) analysis allows us to recover the changes in spectral contributions over time from each kinetically and spectroscopically distinguishable species. For each sample, we find that a single component (i.e., spectrum) and concentration profile describes the time-resolved measurements. If two or more components are modeled, the additional spectra resemble changes within the spectral baseline or random fluctuations in the measurements (See Section S8) and do not contain features consistent with reported CuxOy complexes (vide infra) or the CHA framework.