Quantum chemistry calculation of Al8O12 cluster model for adsorption mechanism of hydrogen fluoride on alumina surface
In this work,the reaction process of alumina adsorption of hydrogen fluoride was studied by using quantum chemical theory.Density functional theory(DFT)was used to study the adsorption behavior of hydrogen fluoride molecule on the surface of cage-like cluster composed of four alumina molecules by using Gaussian.The appropriate approximate structures were obtained by scanning the system composed of alumina cluster and hydrogen fluoride molecule.The actual transition state structure was obtained by further optimization analysis of the structure.Based on this transition state structure,the intrinsic coordinate reaction(IRC)calculation was carried out to determine the adsorption reaction process and simulate the approximate adsorption reactant and product structure.The structures of reactant and product corresponding to both ends of the IRC curve were further optimized.In addition,the energy of reactant,transition state and product in the adsorption process was calculated by Shermo.According to the calculation results,the energy line diagram of the adsorption process was drawn.The bond order was calculated to analyze the change of chemical bond during the adsorption reaction.The results showed that the adsorption of hydrogen fluoride on alumina was chemical adsorption,and the total adsorption energy was-267.5 kJ/mol.There were two continuous stages of the adsorption process.The specific adsorption process was as follows.First,hydrogen fluoride molecule was dissociated.Fluorine atom and hydrogen atom were adsorbed on tricoordinate aluminum atom and its adjacent oxygen atom,respectively.At this time,the alumina cluster underwent certain deformation.Second,the hydrogen atom moved to bicoordinate oxygen atom,surmounted a potential energy barrier,and was adsorbed on it.In the process of hydrogen atom moving,the fluorine atom was adsorbed on the tricoordinate aluminum atom all the time.After the second stage of adsorption,the original deformed cluster was restored.According to the calculated value of the reaction equilibrium constant,it was thought that the adsorption reaction can occur spontaneously at room temperature.
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