Figure 12 . XRD patterns of MnO2-H-200 at different ozone conversion (1, 0.6 and 0.2)
Further evidence on the micro-structural transformation during deactivation was obtained by Raman spectra (Figure 13), which can afford abundant information on short-range structure. For MnO2-H-200, its characteristic peaks were centered at 533 and 665 cm-1, which were attributed to the stretching mode of the Mn-O bond in MnO6 octahedra in β-MnO2. While a new peak at 574cm-1appeared on the spectra of the reacted catalysts, which was indicative of the stretching vibrations of MnO6 octahedra with an interstitial space consisting of (1×2) channels [37-40]. It reflected a formation of γ-MnO2 structure for the reacted catalysts, suggesting that the adsorbed intermediate oxygen species transformed into lattice oxygen. It was further elucidated that the irreversible desorption on MnO2-H-200 led to the loss of active sites and a decay of ozone conversion.