Synthesis of xCe-MnO with three-dimensional ultra-thin nanosheet structure and its excellent low-temperature reducibility for toluene catalysis.

A series of xCe-MnO (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-MnO exhibited the highest catalytic activity for toluene oxidation, with the T of 240 °C. Characterization results from XRD, Raman, SEM, TEM, EDS-mapping, BET, and other techniques reveal that the 0.25Ce-MnO 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-MnO catalyst lead to it excellent toluene transfer ability. Furthermore, compared with MnO, the crystal pattern of 0.25Ce-MnO shifted to the tetragonal cryptomelane type α-MnO phase and exposed more crystal planes which are beneficial to catalyze toluene. H-TPR, O-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 Ce and Mn species, where lattice oxygen played a major role. Moreover, in situ DRIFTS revealed that the 0.25Ce-MnO catalyst showed higher adsorption and desorption capacity for toluene than the MnO 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 MnO. Because 0.25Ce-MnO possesses better ability of converting toluene to benzoate species, it exhibits better activity.