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.