Influence of water molecule on active sites of manganese oxide-based catalysts for ozone decomposition

Developing an efficient approach to decompose ground-level O3 in humidity is crucial for preventing O3 pollution in practical application scenes. In this study, MnOx, CuO, and Cu/MnOx were synthesized to investigate the influence of H2O on the variation of active sites during O3 decomposition. The structural characterizations of the as-synthetic catalysts were measured by N2 physisorption, XRD, SEM, O2-TPD, H2-TPR, TG, and FT-IR analyses. In dry conditions, the elimination rate of O3 followed the sequence of MnOx > Cu/MnOx > CuO. The introduction of Cu to MnOx enhanced the surface area and pore volume of Cu/MnOx, accordingly diminishing the amounts of surface defects and the participation of sub-surface lattice oxygen for catalytic cycle, indicating that surface defects and oxygen vacancies (VO) determined the catalytic activity for O3 decomposition. In humid conditions, the elimination rate of O3 changed to the sequence of Cu/MnOx > MnOx > CuO, with a variation rate compared to dry conditions of −62.9% for MnOx, 14.2% for CuO, and 27.7% for Cu/MnOx. The decrease of participant sub-surface lattice oxygen and the accumulation of intermediates in humidity diminished the decomposition of O3 on MnOx, while the active species such as superoxide radicals generating from the reaction of H2O and Cu/MnOx facilitated the participation of VO and the desorption of O2 from the occupied active sites, accelerating the catalytic cycle on Cu/MnOx. This work developed a deeper understanding of the influence of H2O on catalytic activity, promoting the performance of MnOx-based catalysts for practical O3 decomposition.