The spectral contributions of the independent species formed during O2 activation of Cu-CHA were obtained by multivariate curve resolution-alternating least squares (MCR-ALS) performed in the WiRE™ software package. Iterative fitting procedures, involving up to five components, were used to describe 99.9% of the data. In all cases, greater than 90% of the variance of the measured spectra was described by a single component, while the other extracted spectra primarily represent changes in the baseline during the course of the experiment related to shifts in the sample position or focus over the course of many hours (Section S8).