Adsorption mechanism of As2O3 and Cu-ZSM-5catalysts
The adsorption properties of NO and As2O3 over Cu-ZSM-5surface were calculated based on density functional theory in this paper.By determining the optimum adsorption site of As2O3 over Cu-ZSM-5,the reaction pathway of As3+adsorbed on its active site was investigated,and the activation energy barriers and decisive speed steps of As adsorption reaction on the catalyst were calculated,to reveal the bonding and interaction mechanisms of the reaction between As2O3 and Cu-O-Cu.The results show that the non-oxygen sites of NO and As2O3 are adsorbed on the lattice oxygen sites of active site Cu-O-Cu and the adsorption energies are-218.515kJ/mol and-206.422kJ/mol,respectively.The loss of charge suggests that they interact strongly during adsorption process.The oxidation of As2O3 on lattice oxygen of Cu-O-Cu is divided into two steps.As3+,as Lewis base,is easy to react with Cu-O-Cu as Lewis acid center,and the oxidation product of the first stage,As2O4,undergoes a secondary oxidation reaction at the adjacent active site.As2O5 becomes the main form after As3+adsorption.The reaction pathway to produce As2O4 has to overcome energy barrier of 242.75kJ/mol,which becomes the decisive speed step of the whole oxidation process.
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