The rod-like tetragonal α-MnO 2, flower-like hexagonal ε-MnO 2, and dumbbell-like tetragonal β-MnO 2 were prepared using the hydrothermal or water-bathing method under different conditions. It is shown that the α-MnO 2, ε-MnO 2, and β-MnO 2 catalysts possessed a surface area of ca. 53, 30, and 114 m 2/g, respectively. The oxygen adspecies concentration and low-temperature reducibility decreased in the order of α-MnO 2 > ε-MnO 2 > β-MnO 2, coinciding with the sequence of their catalytic activities for toluene combustion. The well-defined morphological MnO 2 catalysts performed much better than the bulk counterpart. At a space velocity of 20,000 mL/(g h), the temperature for 90% toluene conversion was 238, 229, and 241 °C over α-MnO 2, ε-MnO 2, and β-MnO 2, respectively. The apparent activation energies of α-MnO 2, ε-MnO 2, and β-MnO 2 were in the range of 20-26 kJ/mol. It is concluded that higher oxygen adspecies concentrations and better low-temperature reducibility were responsible for the good catalytic performance of the α-MnO 2, ε-MnO 2, and β-MnO 2 materials.
Scopus Subject Areas
- Process Chemistry and Technology
- Hydrothermal preparation method
- Manganese oxide catalyst
- Toluene combustion
- Water-bathing preparation method
- Well-defined morphology