Synthesis of homogeneous La1 − x Ca x MnO3 solid solutions by the Pechini method and their activity in methane oxidation

Abstract

Homogeneous La1 − x Ca x MnO3 solid solutions have been synthesized by the Pechini method (using polymer-solid compositions). Their microstructure, stability at high temperatures, and catalytic activity in methane oxidation are reported. A continuous series of solid solutions stable in air up to 1100°C forms in the system, and the particle surface is enriched with calcium. A distinctive microstructural feature of the particles is their microporosity. The catalytic activity of all calcium-containing samples (except for x = 0.7) below 700°C is lower than that of lanthanum manganite and decreases under the action of the reaction medium, which can be due to the decrease in the amount of weakly bound oxygen on the surface because of the enrichment of the surface with calcium and the formation of strongly bound surface carbonates. The higher activity and stability of the La0.3Ca0.7MnO3 sample (calcined at 1100°C) above 500°C can be due to the formation of nanosized areas with an Mn3O4 structures on the perovskite particle surface in the reaction medium.