where kapp is the apparent rate constant and [Cu(I)] is the molar density of Cu(I) ions in the Cu-CHA sample. Within Cu-CHA-I, the rate constant for Cu(I) oxidation (kapp,XANES = 1.96 ks -1 ) is 6-times greater than the rate constant to form the CuxOy species observed by Raman spectroscopy (kapp,Raman = 0.31 ks -1 ). Similarly, the rate constants for Cu(I) oxidation within Cu-CHA-M (Figure ; kapp,XANES = 4.01 ks -1 ) are 40-fold greater than rate constant obtained from transients measured by Raman (kapp,Raman = 0.10 ks -1 ). In situ EXAFS after 1 ks reveal that Cu sites in Cu-CHA-M (Table ) and Cu-CHA-I (Table ) are three-coordinate. These spectral features are distinct from those observed in Raman (Figure ) and EXAFS (four-coordinate Cu; Table ) of Cu-CHA-P that contain predominantly Cu(II) before and after contact with O2 (Figure ) as expected for Z2Cu sites that are PMOinactive.