A novel strategy for low-temperature synthesis of Ruddlesden–Popper type layered perovskite La3Mn2O7+δ for methane combustion

Abstract

In comparison to the conventional high-temperature (≥1300 °C) preparation methods, a novel strategy for the synthesis of a Ruddlesden–Popper (R–P) type layered perovskite La₃Mn₂O_7+δ (LLM) at a relatively low temperature (700 °C) was proposed. The conventional perovskite LaMnO₃ (LM) and the nominal La₃Mn₂O_7+δ (NLM) synthesized by the citric acid sol–gel method were compared. Density functional theory calculations were performed to expound the synthesis strategy. The results of X-ray diffraction and high-resolution transmission electron microscopy demonstrated the formation of an R–P type layered perovskite crystal structure in the LLM samples. The results of X-ray photoelectron spectroscopy and hydrogen-temperature-programmed reduction showed that the LLM sample calcined at 700 °C possessed richer and more stable active lattice oxygen species than the other samples because of its two-dimensionally ordered loose intercalated structure. Thus, the LLM samples exhibited excellent thermal stability and higher activity for methane combustion than the LM and NLM samples. After calcination at 1000 °C, the LLM samples still had a relatively higher specific surface area (15.28 m² g⁻¹) than the LM samples (6.64 m² g⁻¹).