A DFT Study Of Surface Properties And Reaction Mechanisms Of NO Oxidation Over Perovskite-type LaCoO₃

Nitrogen oxide?NOx? is harmful to both environment and human health as one of the main air pollutants. It has been a hot spot for people to focus on NOx emission control and elimation. The metal oxides in perovskite-type show the unique structure and well-performing electronic properties, and thus are regarded as a promising substitute for traditional precious metal de-NOx catalysts.Density functional theory?DFT? has been widely applied in theoretical calculation of the electronic properties of solid materials as quantum chemistry develops and progresses. Traditional DFT method has a significant error when dealing with a system with d electrons. People tend to apply DFT+U method to adjust and calibrate the theoretical results in order to make those calculated more consistent with those from experiments.In this dissertation, we conducted a DFT study into the perovskite-type oxide LaCoO₃, making geometrical optimization and analysis of its bulky and surface structure. We compared the outputs of DFT and DFT+U method. The latter method made the gap wider and the formation energy lower than the former, and was more close to the experimental values.We found that the slab with?001? CoO₂ terminal showed a significant energetical stability and surface activity, and was favorable to form surface oxygen vacancy which was the active site of surface reactions. Co3+ ion has three different spin states in different temperatures, which result in the system energy's variety.We studied the energy of the bulk and the surface under the states of low spin, intermediate spin and high spin, and found that the?001? CoO₂ facet showed an excellent performance of oxygen vacancy formation energy, which was of reference for the contrastive experiments under the same range of temperature.The adsorption and interaction of gaseous O₂ and NO molecules on this terminal were studied. O₂ preferred to be adsorbed at the site with which the cobalt ion coordinated to form an octahedrdon. NO molecule transformed to NO₂ species when adsorbed atop the surface lattice oxygen with N-terminal downwards. The species easily desorb and left a surface oxygen vacancy behind.