3.7 Mechanism of deactivation of ozone decomposition
Since the catalytic performance decreased with the reaction time for all MnOx, it is necessary to investigate the catalyst deactivation mechanism to develop more efficient catalyst. The physiochemical performances for MnO2-H-200 before and after reaction were studied. The catalysts, its ozone conversion dropping to 60% and 20%, were denoted as MnO2-H-200-0.6 and MnO2-H-200-0.2, respectively. The surface composition of the catalysts was investigated using XPS (Figure 9). The Mn AOS increased after reaction, accompanied with the binding energy of Mn2p shifting to higher energies, suggesting a higher Mn AOS for deactivated catalysts. And the peak intensity for surface adsorbed oxygen (Oads) increased with the decline of ozone conversion, implying that the oxygen intermediates accumulated on the catalyst surface during the reactions. The intermediates occurring on the partially deactivated catalysts were characterized by FT-IR (Figure S6). The results indicated that a new peak at 1380cm-1 occurred, which was assigned to oxygen species derived from peroxide species O2* [35, 36]. Combined with XPS results, it was speculated that the irreversible O2* desorption on oxygen vacancies led to the accumulation of intermediate oxygen species, resulting in the deactivation of MnO2-H-200.