IFISUR   23398
INSTITUTO DE FISICA DEL SUR
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Influence of the support and oxygen vacancies on the surface reactivity of ZnO (0001)
Autor/es:
W. G. REIMERS; M. A. BALTANÁS; M. M. BRANDA
Reunión:
Congreso; XXXIX Congreso Internacional de Químicos Teóricos de Expresión Latina (QUITEL); 2013
Institución organizadora:
XXXIX Congreso Internacional de Químicos Teóricos de Expresión Latina (QUITEL)
Resumen:
The adsorption of CO, CO2 and H2 molecules on several Zinc oxide surfaces were studied fromInfrared vibrational frequencies by means of DFT calculations. ZnO(0001) perfect and with oxygen vacancies -ZnO(0001)vacO- extended surfaces were the first substrates considered, then, Zinc oxide monolayer grown on CeO2(111) surface was also studied to compare the different surface adsorption properties. The calculations were carried out with the Vienna Ab-Initio Simulation Package (VASP) using the PW91 form of the Generalized Gradient Approximation (GGA) corrected with the so called on-site Hubbard parameter (U). CO and CO2 on ZnO(0001) bind to a surface oxygen atom of the substrate, generating CO2 y CO3, respectively. The C-O bond lengths of these species on the surface are slightly larger than the corresponding free molecules. A slight decrease in the values of the stretching and bending frequencies must be attributed to the interaction with surface. The H2 molecule is absorbed on this surface without dissociating; and the interaction with the substrate is observed by H-H bond weakening, with a decrease of ~ 200 cm-1 in the stretching frequency. On the ZnO(0001)vacO the CO molecule binds to a surface oxygen, adjacent to the vacancy, then forming the CO2 molecule. However,the stretching frequency in this case is ~ 400 cm-1 lower than the isolated molecule value,  indicating a strong interaction with this surface. When we place a CO2 molecule on  ZnO(0001)vacO surface, the most stable configuration is with one of the molecule O atoms occupying the vacancy. The symmetric and antisymetring stretching and bending frequencies are similar to the values corresponding to the isolated CO2 molecule. Both the geometrical configuration and the stretching frequency value for H2 molecule on ZnO(0001)vacO are similar to the ones found for ZnO(0001) perfect surface-which shows a weak interaction. Finally, we found that besides on ZnO(0001) perfect surface, CO and CO2 bind to an oxygen atom in the ZnO(0001) monolayer supported on CeO2, so forming CO2 and CO3= respectively. Symmetric and antisymmetric stretching frequency values are lower in this case, which would indicate a significant interaction with the surface. Reaction of the H2 molecule on the supported ZnO monolayer is relevant since, in this case, the molecule breaks up and spontaneously form H2O. Ifwe compare these values with the ones obtained for free water molecule, we see that the former are smaller by ~300 cm-1 consequently we infer that the binding of this molecule to the substrate is strong.