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 m2/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. 3DOM-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/O2 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 °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.

Graphical abstractBy using the PEG- and/or l-lysine-aided PMMA-templating strategy, we prepared three-dimensionally ordered macroporous (3DOM) LaMnO3 with mesoporous skeletons. It is found that the excellent catalytic performance of porous LaMnO3 for toluene combustion was associated with the high surface area and oxygen adspecies concentration, good low-temperature reducibility, and unique bimodal pore structure.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► 3DOM LaMnO3 with mesoporous walls are prepared by l-lysine-aided PMMA-templating method. ► l-Lysine addition is critical in the formation of 3DOM structure with mesoporous skeletons. ► Bimodal porous LaMnO3 possess high surface area and oxygen adspecies content and good reducibility. ► 3DOM LaMnO3 with mesoporous walls perform excellently in the combustion of toluene. ► Catalytic activity is related to surface area, oxygen adspecies, reducibility, and bimodal pore structure.