Catalytic potential of ceria decorated with mixed manganese oxides for oxidation of aromatic volatile organic compounds

Cerium(IV) oxide, CeO₂, is widely used as a catalyst due to its high oxygen storage and release capacity, high oxygen mobility, and thermal stability, which contribute to its high catalytic activity in many oxidation reactions. At the same time, volatile organic compounds (VOCs) are among the major air pollutants emitted from numerous industrial processes and commercial products, and can have harmful effects on both human health and the environment. Therefore, the development of efficient catalysts for their oxidation is an important research topic. In this study, pure and decorated cerium(IV) oxide catalysts were prepared, characterised, and evaluated for the catalytic oxidation of benzene and toluene as model VOCs. Pure CeO₂ was synthesised using a soft-template sol-gel method, while the decorated samples were prepared by applying aqueous solutions of precursor nitrate salts of manganese, iron, copper and nickel (in molar ratios of Mn:M=1:1, M=Fe, Cu, Ni) via wet impregnation. After impregnation, the samples were dried at 100 °C for 1 hour to remove excess water and then calcined for 2 h at 500 °C, producing a stable layer of catalytically active mixed manganese oxides (MnFeO_x, MnCuO_x, and MnNiO_x). Pure CeO₂ and the decorated catalysts were characterised with various methods to analyse and confirm their composition, and to assess the adhesion of the catalyst layer to the CeO₂ particles. Catalytic activity testing was carried out in a reactor system using gas mixtures (Messer) of benzene/N₂ and toluene/N₂, with on-line gas chromatography used to monitor the catalytic oxidation. All three decorated CeO₂ catalysts showed excellent performance and high efficiency in the catalytic oxidation of benzene and toluene, achieving conversions of >99% at temperatures below 230 °C.