Synthesis of xCe-MnO₂ with three-dimensional ultra-thin nanosheet structure and its excellent low-temperature...

A series of xCe-MnO₂ (x = 0-1) catalysts were synthesized using ammonium oxalate as a precipitator via the redox precipitation method and hydrothermal synthesis method. The results indicate that 0.25Ce-MnO₂ exhibited the highest catalytic activity for toluene oxidation, with the T₉₉ of 240 °C. Characterization results from XRD, Raman, SEM, TEM, EDS-mapping, BET, and other techniques reveal that the 0.25Ce-MnO₂ catalyst exhibited a three-dimensional multistage ultrathin nanosheet structure by adjusting the introduction amount of Ce, with abundant active sites, and effectively formed Ce-Mn homogeneous dispersion. The larger pore size and volume of 0.25Ce-MnO₂ catalyst lead to it excellent toluene transfer ability. Furthermore, compared with MnO₂, the crystal pattern of 0.25Ce-MnO₂ shifted to the tetragonal cryptomelane type α-MnO₂ phase and exposed more crystal planes which are beneficial to catalyze toluene. H₂-TPR, O₂-TPD, and XPS characterization further confirmed the strong interaction between Ce and Mn oxides, which exhibited better low-temperature reducibility and oxygen migration, along with abundant Ce³⁺ and Mn³⁺ species, where lattice oxygen played a major role. Moreover, in situ DRIFTS revealed that the 0.25Ce-MnO₂ catalyst showed higher adsorption and desorption capacity for toluene than the MnO₂ catalyst, and benzoate species were the key intermediates for catalytic oxidation. Additionally, benzoate and surface phenolic species were the key intermediates for catalytic oxidation of MnO₂. Because 0.25Ce-MnO₂ possesses better ability of converting toluene to benzoate species, it exhibits better activity.