Lysine-aided PMMA-templating preparation and high performance of three-dimensionally ordered macroporous LaMnO3 with mesoporous walls for the catalytic combustion of toluene

Rhombohedrally crystallized three-dimensionally ordered macroporous (3DOM) perovskite-type oxides LaMnO3 with mesoporous skeletons were prepared using the poly(ethylene glycol) (PEG)- and/or L-lysine-assisted poly(methyl methacrylate) (PMMA)-templating method. Physicochemical properties of the materials were characterized by numerous analytical techniques. Catalytic performance of the as-prepared LaMnO3 samples was evaluated for the combustion of toluene. It is found that addition of appropriate amounts of PEG400 and L-lysine was beneficial for the generation of high-quality 3DOM-structured LaMnO3 (denoted as LaMnO3-PL-1, LaMnO3-PL-2, and LaMnO3-PL-3 derived with a PEG400/L-lysine molar ratio of 1.23, 0.61, and 0.31, respectively) with mesoporous skeletons and high surface areas (32-38 m(2)/g). Among the LaMnO3 samples, the LaMnO3-PL-2 one possessed the largest surface area and the highest contents of surface Mn4+ and adsorbed oxygen species. 300M-structured LaMnO3 showed better low-temperature reducibility than bulk LaMnO3, with the LaMnO3-PL-2 sample displaying the best low-temperature reducibility. 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 LaMnO3 catalysts remarkably outperformed the nonporous bulk counterpart; over the best-performing LaMnO3-PL-2 catalyst, the temperatures required for toluene conversion = 50 and 90% were ca. 226 and 249 degrees C, respectively. The apparent activation energies (58-61 kJ/mol) for toluene combustion over the LaMnO3-PL-1-3 catalysts were much lower than that (97 kJ/mol) over the bulk LaMnO3 catalyst. It is concluded that the large surface area, high oxygen adspecies content, good low-temperature reducibility, and unique bimodal pore structure were responsible for the good performance of 3DOM-architectured LaMnO3 with mesoporous skeletons for toluene combustion. (C) 2012 Elsevier BM. All rights reserved.