Heterolytic adsorption of H2 on ZnO(101 over-bar 0) surface: An ab initio SPC cluster model study

摘要

Heterolytic adsorption of H_2 on ZnO(101 over-bar 0) surface has been investigated by means of ab initio embedded cluster method. The embedding point charges are spherically expanded, while the values of the spherical charges are determined to be self-consistent with those of the atoms in the cluster. Several possible adsorption sites have been considered with Zn_5O_5 and Zn_4O_4, which are the stoichiometric clusters having the least amount of dangling bonds in the given size. The effect of the shape of the embedding spherical charge array and the influence of the surface reconstruction on the calculated adsorption properties have been investigated. The calculation results show that the heterolytic adsorption of H_2 on ZnO(101 over-bar 0) surface is site-dependent, taking place only on those Zn-O ion-pairs with low coordination numbers, such as Zn_(2c)-O_(3c), Zn_(3c)-O_(2c), and Zn_(2c)-O_(2c), rather than on the perfect ion pair, Zn_(3c)-O_(3c). The calculated adsorption heats, as well as vibrational frequencies of the Zn-H and O-H bonds, are in reasonable agreement with the experimental values.