Controlled preparation and high catalytic performance of three-dimensionally ordered macroporous LaMnO ₃ with nanovoid skeletons for the combustion of toluene

Three-dimensionally ordered macroporous (3DOM) single-phase rhombohedral perovskite-type oxide LaMnO ₃ materials with nanovoid skeletons were prepared using the poly(methyl methacrylate)-templating methods with the assistance of surfactant (poly(ethylene glycol) (PEG) or triblock copolymer (Pluronic P123)). The nature of surfactant influenced the pore structure of the LaMnO ₃ sample. The use of PEG400 alone led to a 3DOM-structured LaMnO ₃ without nanovoid skeletons; with the addition of PEG400 and P123, however, one could prepare LaMnO ₃ samples with high-quality 3DOM structures, nanovoid skeletons, and high surface areas (37-39 m ²/g). Under the conditions of toluene concentration = 1000 ppm, toluene/O ₂ molar ratio = 1:400, and space velocity = 20,000 mL/(g h), the porous LaMnO ₃ samples were superior to the bulk counterpart in catalytic performance, with the nanovoid-containing 3DOM-structured LaMnO ₃ catalyst performing the best (the temperatures for toluene conversions of 50% and 90% were 222-232 and 243-253 °C, respectively). The apparent activation energies (57-62 kJ/mol) over the 3DOM-structured LaMnO ₃ catalysts were much lower than that (97 kJ/mol) over the bulk LaMnO ₃ catalyst. We believe that the excellent performance of the 3D macroporous LaMnO ₃ materials in catalyzing the combustion of toluene might be due to factors such as large surface area, high oxygen adspecies concentration, good low-temperature reducibility, and unique nanovoid-containing 3DOM structure of the materials.