Complex Catalytic Materials Based on the Perovskite-Type Structure for Energy and Environmental Applications

Investigation of Catalytic and Photocatalytic Degradation of Methyl Orange Using Doped LaMnO3 Compounds

LaMnO3 and 1% Pd-, Ag-, or Y-doped perovskite type nanomaterials were prepared by the sol-gel method, followed by heat treatment at a low temperature (600 °C for 6 h). The investigation through X-ray diffraction and FT-IR spectroscopy indicated that all samples were well crystallized, without secondary phases, and that the transition metal doping changed the crystal structure from the R-3c space group for the undoped LaMnO3 to the Pm-3m space group for the doped perovskite compounds. In this research paper, the efficiencies of the perovskite LaMnO3 materials for methyl orange removal were analyzed, wherein the effect of the doping ions and of the pH on the catalytic activity were studied together with a kinetic approach for the LaMnO3 materials at different values of the pH. Moreover, in the catalytic activity, it should be noted that a slightly better performance was obtained for the Ag-doped materials compared to the Y- and Pd-doped perovskite samples. The results presented for the perovskite LaMnO3 nanomaterials reinforce the interest in these multifunctional materials to be used in industrial applications; e.g., in water treatment.

Progress and Recent Strategies in the Synthesis and Catalytic Applications of Perovskites Based on Lanthanum and Aluminum

Lanthanum aluminate-based perovskite (LaAlO₃) has excellent stability at high temperatures, low toxicity, and high chemical resistance and also offers wide versatility to the substitution of La³⁺ and Al³⁺, thus, allowing it to be applied as a catalyst, nano-adsorbent, sensor, and microwave dielectric resonator, amongst other equally important uses. As such, LaAlO₃ perovskites have gained importance in recent years. This review considers the extensive literature of the past 10 years on the synthesis and catalytic applications of perovskites based on lanthanum and aluminum (LaAlO₃). The aim is, first, to provide an overview of the structure, properties, and classification of perovskites. Secondly, the most recent advances in synthetic methods, such as solid-state methods, solution-mediated methods (co-precipitation, sol–gel, and Pechini synthesis), thermal treatments (combustion, microwave, and freeze drying), and hydrothermal and solvothermal methods, are also discussed. The most recent energetic catalytic applications (the dry and steam reforming of methane; steam reforming of toluene, glycerol, and ethanol; and oxidative coupling of methane, amongst others) using these functional materials are also addressed. Finally, the synthetic challenges, advantages, and limitations associated with the preparation methods and catalytic applications are discussed.