Synthesis of x Ce–MnO 2 with three-dimensional ultra-thin nanosheet structure and its excellent low-temperature reducibility for toluene catalysis

A series of x Ce-MnO 2 ( 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 2 exhibited the highest catalytic activity for toluene oxidation, with the T 99 of 240 °C. Characterization results from XRD, Raman, SEM, TEM, EDS-mapping, BET, and other techniques reveal that the 0.25Ce-MnO 2 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 2 catalyst lead to it excellent toluene transfer ability. Furthermore, compared with MnO 2 , the crystal pattern of 0.25Ce-MnO 2 shifted to the tetragonal cryptomelane type α-MnO 2 phase and exposed more crystal planes which are beneficial to catalyze toluene. H 2 -TPR, O 2 -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 3+ and Mn 3+ species, where lattice oxygen played a major role. Moreover, in situ DRIFTS revealed that the 0.25Ce-MnO 2 catalyst showed higher adsorption and desorption capacity for toluene than the MnO 2 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 2 . Because 0.25Ce-MnO 2 possesses better ability of converting toluene to benzoate species, it exhibits better activity.