Low-Temperature Synthesis of Ruddlesden–Popper Type Layered Perovskite La_xCa_3−xMn₂O₇ for Methane Combustion

Abstract

In comparison to the conventional high temperature (≥1,300 °C) preparation conditions, a series of Ruddlesden–Popper (R–P) type layered perovskite La_xCa_3−xMn₂O₇ (x = 0.8, 1.0, 1.2, 1.5, 2.0, 2.5, and 3.0) were synthesized at 700 °C by an improved method based on the strategy involving the “inductive effect of Cl”. XRD results revealed the unitary R–P type layered perovskite structure in the samples of x = 0.8, 1.0, 1.2, and 3.0. While in the samples of x = 1.5, 2.0, and 2.5, the layered perovskite phase and lanthanum oxide phase coexisted, which resulted in their poor redox properties. XPS and H₂-TPR results demonstrated that the redox properties of La_xCa_3−xMn₂O₇ were correlated with its structural integrity and purity and influenced by the x value. The sample of x = 1.2 gave the highest methane combustion activity with T ₅₀ = 449 °C, and the sample of x = 2.0 showed the lowest activity with T ₅₀ = 538 °C, which was in accordance with the XPS and H₂-TPR results. The specific surface areas of La_xCa_3−xMn₂O₇ depended on the x value monotonically, and the sample of x = 0.8 presented the highest surface area value (33.59 m² g⁻¹).