Efficient ozone decomposition over nickel-modified amorphous MnO_x catalysts

Manganese oxides (MnO_x) with crystal structures are difficult to effectively remove ozone under high humidity owing to their low defect content and poor moisture resistance. Herein, Ni_a-MnO_x-A catalysts with different defect degrees were well fabricated by modulating the ratios of the precursors via a facile hydrothermal approach. Effects of molar ratios of precursors on physiochemical properties and ozone removal efficiencies of Ni_a-MnO_x-A were investigated systematically under high humidity conditions. Amorphous Ni_0.5-MnO_x-1.5 exhibited an ozone conversion of 100% for a continuous air flow containing 20 ppm ozone at a relative humidity (RH) of 60% (space velocity = 600 L·g⁻¹·h⁻¹). The incorporation of Ni²⁺ ions weakened the crystallinity and facilitated oxygen vacancy defect formation, which are believed to be active sites for ozone decomposition. It was confirmed that the exceptional ozone decomposition capacity of Ni_0.5-MnO_x-1.5 was attributed to its abundant oxygen vacancy, larger specific surface area, and higher reducibility and oxygen mobility. Furthermore, sufficient oxygen vacancy effectively mitigated the negative effect of humidity.