A comparison of CO oxidation on cleaned ZnO surface and defective ZnO surface using density functional theory studies

In this work, we employed continuously the DFT calculations to study CO oxidation reaction on the defective ZnO $$ surface. The oxygen (O) atom was removed from cleaned surface ZnO $$(CS-ZnO) to form the defective ZnO $$ surface (DS-ZnO), which contained an O vacancy defect. Hereafter, the formation of oxygen vacancy was found to increase the adsorption abilities of O₂ and CO on DS-ZnO, in comparison to those on CS-ZnO. Many steps of elementary reactions including O₂ and CO adsorption, reacting between CO and O to form CO₂, and CO₂ desorption on DS-ZnO were investigated and calculated in terms of the configurations, activation energy, and reaction energy, to which the reaction pathway of CO oxidation has been found. Based on this pathway, the calculation results of the rate controlling step of 0.84 eV corresponding to the exothermic reaction energy of 4.11 eV on DS-ZnO indicated that the CO oxidation on DS-ZnO was more thermodynamically favorable and less kinetically desirable than that on CS-ZnO. In addition, the natural bonds of O₂ and CO adsorptions on DS-ZnO were also analyzed by the partial density of state (PDOS) and the electron density difference (EDD) contour plots.