Role of interfacial effects in the oxidation of toluene by MnO_x-modified CeO₂ nanocubes

Toluene, a common volatile organic compounds (VOCs), can have adverse effects on the natural environment as well as on human health. Catalytic oxidation technology can remove toluene economically and efficiently, and the key to this technology is the development of efficient catalysts. In order to improve the oxidation efficiency of toluene, it is of great significance to explore and study new efficient catalysts. In this study, binary xMn/Ce (xMnO_x/CeO₂) catalysts with different Mn loadings were successfully prepared by a two-step hydrothermal-impregnation method, and the performance of these catalysts was evaluated in the catalytic oxidation reaction of toluene. The results showed that the introduction of MnO_x significantly increased the toluene oxidation activity of the catalysts. In particular, when the Mn loading was 10% (10Mn/Ce), the t₉₀ (temperature at which toluene conversion reached 90%) was only 233 ℃ at gas hourly space velocity of 60000 mL/(g·h), showing optimal toluene catalytic oxidation activity. This result suggests that the addition of moderate amount of MnO_x can significantly improve the catalytic performance of the catalysts. By characterization means such as X-ray diffraction (XRD), Raman, transmission electron microscopy (TEM), programmed temperature-raising reduction (H₂-TPR), and X-ray photoelectron spectroscopy (XPS), we found that the incorporation of MnO_x creates an interfacial effect between MnO_x and CeO₂, which significantly alters the physicochemical properties of the Mn/Ce catalysts. Due to the interfacial effect, the concentration of Ce³⁺ and Mn³⁺ ions and the oxygen vacancy in the 10Mn/Ce catalyst were not only increased, but also the strength of Ce−O bond on the catalyst surface was reduced, which made it easier for surface lattice oxygen to participate in the catalytic oxidation of toluene, and enhanced the redox performance of the catalyst, thus promoting the catalytic oxidation of toluene. In this study, we not only successfully prepared Mn/Ce catalysts with excellent toluene oxidation activity, but also revealed the mechanism of interfacial effect behind it, which provides a simple and effective method and idea for the design and preparation of efficient oxidation catalysts for VOCs.