Effect of the preparation method on the catalytic activity of La1−xCaxFeO3 perovskite-type oxides

Precursor accumulation on nanocarbons for the synthesis of LaCoO3 nanoparticles as electrocatalysts for oxygen evolution reaction

Oxygen evolution reaction (OER) is a key step in energy storage devices. Lanthanum cobaltite (LaCoO₃) perovskite is an active catalyst for OER in alkaline solutions, and it is expected to be a low-cost alternative to the state-of-the-art catalysts (IrO₂ and RuO₂) because transition metals are abundant and inexpensive. For efficient catalysis with LaCoO₃, nanosized LaCoO₃ with a high surface area is desirable for increasing the number of catalytically active sites. In this study, we developed a novel synthetic route for LaCoO₃ nanoparticles by accumulating the precursor molecules over nanocarbons. This precursor accumulation (PA) method for LaCoO₃ nanoparticle synthesis is simple and involves the following steps: (1) a commercially available carbon powder is soaked in a solution of the nitrate salts of lanthanum and cobalt and (2) the sample is dried and calcined in air. The LaCoO₃ nanoparticles prepared by the PA method have a high specific surface area (12 m² g⁻¹), comparable to that of conventional LaCoO₃ nanoparticles. The morphology of the LaCoO₃ nanoparticles is affected by the nanocarbon type, and LaCoO₃ nanoparticles with diameters of less than 100 nm were obtained when carbon black (Ketjen black) was used as the support. Further, the sulfur impurities in nanocarbons significantly influence the formation of the perovskite structure. The prepared LaCoO₃ nanoparticles show excellent OER activity owing to their high surface area and perovskite structure. The Tafel slope of these LaCoO₃ nanoparticles is as low as that of the previously reported active LaCoO₃ catalyst. The results strongly suggest that the PA method provides nanosized LaCoO₃ without requiring the precise control of chemical reactions, harsh conditions, and/or special apparatus, indicating that it is promising for producing active OER catalysts at a large scale.

A simple synthetic process for LaCoO₃ nanoparticles based on the accumulation of precursors on nanocarbon supports was presented. The LaCoO₃ nanoparticles showed excellent OER activity owing to their high surface area and perovskite structure.

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

This review paper focuses on perovskite-type materials as (photo)catalysts for energy and environmental applications. After a short introduction and the description of the structure of inorganic and hybrid organic-inorganic perovskites, the methods of preparation of inorganic perovskites both as powders via chemical routes and as thin films via laser-based techniques are tackled with, for the first, an analysis of the influence of the preparation method on the specific surface area of the material obtained. Then, the (photo)catalytic applications of the perovskites in energy production either in the form of hydrogen via water photodecomposition or by methane combustion, and in the removal of organic pollutants from waste waters, are reviewed.

Low-temperature wet chemistry synthetic approaches towards ferrites

Solution chemistry allows the crystallisation of range of iron oxides, including MFe₂O₄ spinels, MFeO₃ perovskites and hexaferrites, such as BaFe₁₂O₁₉, with nanoscale crystallinity and properties suitable for fields such as catalysis and electronics.

Dry Reforming of Methane over NiLa-Based Catalysts: Influence of Synthesis Method and Ba Addition on Catalytic Properties and Stability

CO2 reforming of CH4 to produce CO and H2 is a traditional challenge in catalysis. This area is still very active because of the potentials offered by the combined utilization of two green-house gases. The development of active, stable, and economical catalysts remains a key factor for the exploitation of natural gas (NG) with captured CO2 and biogas to produce chemicals or fuels via syngas. The major issue associated with the dry reforming process is catalyst deactivation by carbon deposition. The development of suitable catalyst formulations is one strategy for the mitigation of coking which becomes especially demanding when noble metal-free catalysts are targeted. In this work NiLa-based catalyst obtained from perovskite precursors La1−xBaxNiO3 (x = 0.0; 0.05; 0.1 and 0.2) and NiO/La2O3 were synthesized, characterized by in situ and operando XRD and tested in the dry reforming of methane. The characterization results showed that the addition of barium promoted BaCO3 segregation and changes in the catalyst structure. This partly affected the activity; however, the incorporation of Ba improved the catalyst resistance to deactivation process. The Ba-containing and Ba-free NiLa-based catalysts performed significantly better than NiO/La2O3 catalysts obtained by wet impregnation.

A perovskite oxide with a tunable pore-size derived from a general salt-template strategy as a highly efficient electrocatalyst for the oxygen evolution reaction

A porous perovskite oxide is fabricated by an inorganic salt-template strategy, which exhibits remarkable performance for the oxygen evolution reaction.

The influence of Ca substitution on LaFeO3 nanoparticles in terms of structural and magnetic properties

BACKGROUND

The nanocrystalline structure of La_{1 -x}Ca _xFeO₃ was prepared by a sol-gel method involving an auto-combustion process. The incorporation of rare-earths in LaFeO₃ induces strain in magnetic properties, especially in terms of the following parameters: replacement amount, oxygen partial pressure, and calcination temperature.

METHODS

To determine the effects of the amount of Ca²⁺ ion doping agent and the calcination temperature on the microstructure, particle morphology, and magnetic properties of LaFeO₃ crystal, we performed the following respective analytical methods: X-ray powder diffraction, Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy, and vibrating sample magnetometer tests.

RESULTS

The orthorhombic structure of LaFeO₃ perovskite did not change even when it was doped with Ca²⁺ ions, and its space group continued to be Pnma (No.62). FT-IR spectra confirmed that the main band appearing at 568 cm^-1 is due to the antisymmetric stretching vibration of Fe-O-Fe bonds in FeO₆. The introduction of Ca inhibits the growth of grains but the morphology of particles is improved. With an increasing concentration of Ca²⁺ ions, magnetic behavior of the samples also witnessed an increasing trend in a proportionate manner. With an increase in calcination temperature, the enclosed area of the magnetic hysteresis curve of the sample reduced remarkably.

CONCLUSIONS

The growth of nanoparticles can be restrained with an increase of Ca content that is used as doping agent. The magnetic behavior of La_{1 -x}Ca _xFeO₃ tilts towards G-type antiferromagnetism; the magnetic orientation is achieved from the super exchange interaction of Fe³⁺ ions with oxygen ions.

Improved catalytic activity of PrMO3 (M = Co and Fe) perovskites: synthesis of thermally stable nanoparticles by a novel hydrothermal method

A simple hydrothermal method was used to synthesize nanoperovskites using metal cyano complexes as precursors.

Improved low-temperature activity of La–Sr–Co–O nano-composite for CO oxidation by phase cooperation

La_0.7–Sr_0.3–Co–O nano-composite shows improved catalytic activity to CO oxidation relative to La_0.7Sr_0.3CoO₃ and Co₃O₄, which is suggested to be due to a synergistic effect induced by the phase cooperation.