A comparison of water-gas shift reaction on ZnO [Formula: see text] surface and 6Cu cluster deposited over ZnO [Formula: see text] surface using density functional theory studies.

This work has presented a calculated study of the water-gas shift reaction (WGSR) performing on the models of ZnO [Formula: see text] only and six-atomic copper cluster deposited on the ZnO surfaces (6Cu/ZnO) using density functional theory (DFT). The most stable configurations of ZnO and 6Cu/ZnO surfaces were found and used for the mechanism calculations of WGSR. The carboxyl mechanism of WGSR was proposed to find the reaction pathway. Based on this pathway, WGSR occurred at the elementary reaction of COOH intermediate formation as the rate-controlling step on 6Cu/ZnO surface, and the elementary reaction of H-H association as the rate-controlling step on ZnO surface, in which the highest activation energies were calculated as 1.05 eV and 1.56 eV for 6Cu/ZnO and ZnO surfaces, respectively. These calculations indicated that the 6Cu/ZnO was more favorable and more effective than ZnO as a catalyst for WGSR. In addition, the nature of bonds of CO and H2O adsorption on ZnO and 6Cu/ZnO surfaces was also analyzed using the local density of states (LDOS) and electron density difference (EDD) methods.

A comparison of CO oxidation on cleaned ZnO [Formula: see text] surface and defective ZnO [Formula: see text] surface using density functional theory studies.

In this work, we employed continuously the DFT calculations to study CO oxidation reaction on the defective ZnO [Formula: see text] surface. The oxygen (O) atom was removed from cleaned surface ZnO [Formula: see text] (CS-ZnO) to form the defective ZnO [Formula: see text] 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.