Material properties of perovskites in the quasi-ternary system LaFeO3–LaCoO3–LaNiO3

LaNiO3 Perovskite Synthesis through the EDTA–Citrate Complexing Method and Its Application to CO Oxidation

A series of LaNiO3 materials were synthesized by the EDTA–citrate complexing method, modifying different physicochemical conditions. The LaNiO3 samples were calcined between 600 and 800 °C and characterized by XRD, SEM, XPS, CO-TPD, TG, DT, and N2 adsorption. The results evidence that although all the samples presented the same crystal phase, LaNiO3 as expected, some microstructural and superficial features varied as a function of the calcination temperature. Then, LaNiO3 samples were tested as catalysts of the CO oxidation process, a reaction never thoroughly analyzed employing this material. The catalytic results showed that LaNiO3 samples calcined at temperatures of 600 and 700 °C reached complete CO conversions at ~240 °C, while the sample thermally treated at 800 °C only achieved a 100% of CO conversion at temperatures higher than 300 °C. DRIFTS and XRD were used for studying the reaction mechanism and the catalysts’ structural stability, respectively. Finally, the obtained results were compared with different Ni-containing materials used in the same catalytic process, establishing that LaNiO3 has adequate properties for the CO oxidation process.

A First Principles Study of H₂ Adsorption on LaNiO₃(001) Surfaces

The adsorption of H₂ on LaNiO₃ was investigated using density functional theory (DFT) calculations. The adsorption sites, adsorption energy, and electronic structure of LaNiO₃(001)/H₂ systems were calculated and indicated through the calculated surface energy that the (001) surface was the most stable surface. By looking at optimized structure, adsorption energy and dissociation energy, we found that there were three types of adsorption on the surface. First, H₂ molecules completely dissociate and then tend to bind with the O atoms, forming two –OH bonds. Second, H₂ molecules partially dissociate with the H atoms bonding to the same O atom to form one H₂O molecule. These two types are chemical adsorption modes; however, the physical adsorption of H₂ molecules can also occur. When analyzing the electron structure of the H₂O molecule formed by the partial dissociation of the H₂ molecule and the surface O atom, we found that the interaction between H₂O and the (001) surface was weaker, thus, H₂O was easier to separate from the surface to create an O vacancy. On the (001) surface, a supercell was constructed to accurately study the most stable adsorption site. The results from analyses of the charge population; electron localization function; and density of the states indicated that the dissociated H and O atoms form a typical covalent bond and that the interaction between the H₂ molecule and surface is mainly due to the overlap-hybridization among the H 1s, O 2s, and O 2p states. Therefore, the conductivity of LaNiO₃(001)/H₂ is stronger after adsorption and furthermore, the conductivity of the LaNiO₃ surface is better than that of the LaFeO₃ surface.