These comparisons demonstrate three critical points with broad significance for stoichiometric and catalytic oxidation reactions performed over Cu exchanged zeolites. First, Cu ions oxidize quickly to form Cu(II) and the majority of Cu exists as Cu(II) within 2 ks. Consequently, the CuxOy species responsible for the Raman scattering features (Figure ) must correspond to a Cu(II) complex. Second, changes observed by Raman over longer timescales suggest that following a rapid oxidation of Cu(I) to Cu(II) the structure of the Cu complexes continue to evolve through subsequent processes that occur at slower rates to form the Raman active CuxOy species. Third, yields of CH3OH formed by PMO continue to increase well after the Cu(I) to Cu(II) transition period and correlate strongly with the numbers of the Raman-resonant CuxOy complexes, which suggests this CuxOy species are linked to the active intermediates responsible for partial methane oxidation.