Co2+ substituted La2CuO4/LaCoO3 perovskite nanocomposites: synthesis, properties and heterogeneous catalytic performance

Abstract

Cobalt substituted La₂CuO₄/LaCoO₃ perovskite nanocomposites were prepared using a microwave combustion method. X-ray diffraction analysis showed that Co²⁺ substitution in La₂CuO₄ induced the formation of a secondary LaCoO₃ phase with rhombohedral structure along with the existing orthorhombic (La₂CuO₄) structure. The orthorhombic/rhombohedral structured nanocomposites possessed an average crystallite size in the range of 36–46 nm and 21–49 nm, respectively. The Rietveld analysis confirmed the formation of these two phases. The appearance of FT-IR bands around 682 and 512 cm⁻¹ was correlated to the orthorhombic stretching modes while the bands around 580 and 445 cm⁻¹ were associated with the rhombohedral stretching modes thereby confirming the two-phase perovskite system. An optical study revealed two linear regions depicting two band gaps related to the La₂CuO₄ and LaCoO₃ phases. The band gap was found to increase with an increase in the Co²⁺ doping fraction. Morphological observations using scanning electron microscopy showed intragranular pores and fused grains with distinct grain boundaries. The change in the magnetic properties was associated most probably with the exchange of the A and B sites within the La₂CuO₄ host lattice because of Co²⁺ doping, as well as the important phase composition of La₂CuO₄/LaCoO₃ obtained from the ferromagnetic-to-paramagnetic transition. The BET surface area of the pure and doped nanocomposites was found to vary considerably within the range of 12.2–43.7 m² g⁻¹. The as-fabricated La₂CuO₄/LaCoO₃ perovskite nanocomposites were evaluated for the conversion of glycerol to formic acid in a liquid phase batch reactor under atmospheric conditions. This La³⁺ based nanocomposite behaves as an efficient bifunctional catalyst with high conversion efficiency and selectivity around 96.5% and 95.1%, respectively.