Fig. 6. Quantification of Cu compounds during the in situ Cu K-edge XANES measurements from linear combination fits, using the reference spectra shown in Fig. 2. Upper panels: R-factors of the linear combination fits. Lower panels: concentration profiles for the different Cu species during reduction in NH₃ + NO, the formation of the [Cu₂^II(NH₃)₄O₂]²⁺ complex, and consequent exposures of the [Cu₂^II(NH₃)₄O₂]²⁺ complex to SO₂ and O₂, for the low-Cu (left) and high-Cu (right) catalysts.