4. Conclusions
A series of MnOx catalysts (MnO2, Mn2O3 and Mn3O4) with different Mn valences were synthesized by calcining γ-MnOOH through tuning the calcination temperature and atmosphere. MnO2-H-200 was obtained by reducing MnO2 using hydrogen. The catalytic activity of the above MnOx towards ozone decomposition followed the order of MnO2-H-200 >MnO2> Mn2O3> Mn3O4.MnO2 showed better activity than Mn2O3 and Mn3O4 due to its lower formation energy of oxygen vacancy and desorption energy of peroxide species. Especially among three catalysts, the least desorption energy of peroxide species on MnO2 facilitated to the occurrence of rate-limiting reaction step. The surface oxygen vacancy got enriched for MnO2-H-200 by H2-reduction. The results elucidated that both the nature and abundance of oxygen vacancies have a decisive influence on the catalytic decomposition of ozone. Take an example of MnO2-H-200, the insights on deactivation mechanism further validated that the catalytic stability of O3 decomposition was strongly associated with the regeneration capacity of oxygen vacancy. The transformation from adsorbed oxygen species to lattice oxygen led to an irreversible generation of oxygen vacancy, which changed the property of the surface of the catalysts and resulted in the difficult desorption of O2*. Hence it caused the deactivation of the catalyst.