An Investigation Of Adsorption Mechanism For CH₄ High-temperature Catalytic Inflammation

In this paper,quantum chemistry theory was employed to evaluate high temperature reaction of CH₄ and O₂ on the surface of perovskite.The work was focused on the effect of different surface of perovskite on the catalytic activities.In addition,the catalytic properties of a various concentration of La doped ABO₃ also were investigated.During this calculation,density functional theory of the first principle was adopted to study the periodic structure of the catalysts.Perovskite BaZrO₃ was taken as a model to build vacuum surface for electronic structure and reaction mechanism analysis of CH₄ and O₂ adsorption on the catalysts.Firstly,the stable surface of BaZrO₃ was searched by structure optimization.The electronic structures and surface structures of BaZrO₃ were investigated.The results showed the charge in the surface was redistributed.The energy of BaZrO₃(001) is lower than BaZrO₃(011) and BaZrO₃(111).The(001) surface of BaZrO₃ was demonstrated to be most stable. Second,CH₄ and O₂ molecules were placed in different position of the surface to calculate properties and optimize structure.The effect of A and B ion(ABO₃) for adsorption behavior of CH₄ and O₂ on the surface were investigated by confirming the most suitable absorption position.The absorbing mechanism was reasoned by population and electron states analysis.The most favorite adsorption site was located at B site of the catalysts.Comparing CH₄ and O₂ absorbed on different perovskites surface,it was found that the different A could adjust the charge of B ion and affect the adsorption behavior of CH₄ and O₂.The order of the activity of methane burning were as follows:LaCoO₃＞BaZrO₃＞BaCeO₃＞BaCoO₃.The calculated results were consistent with the previous reference reports.Due to the adsorption of gas is the key step of catalytic combustion reaction,it can deduce the main oxidant is the O₂ adsorbed on the surface of catalyst in this process.The stronger of adsorption of CH₄ and O₂ is,the better the catalyst.Third,the crystal structure,electronic states and bond population of catalyst for a various concentration of La doped ABO₃ were calculated in order to comprehensive catalytic activation of La replaced A atom.It was expected to obtain further effect of A and B ion on the adsorption behavior of CH₄ and O₂ molecules on the surface of perovskite.The results of this works could provide the basement of the credible theory for the design of new-type CH₄ inflammation catalyst with high-acticity and high-stability.