CO adsorption on Ni, Pd, Cu and Ag deposited on MgO, CaO, SrO and BaO: Density functional calculations

摘要

The adsorption properties of CO molecules adsorbed on Ni, Pd, Cu and Ag atoms deposited on O~(2-), F and F~+ sites of MgO, CaO, SrO and BaO terrace surfaces have been studied by means of density functional calculations and embedded cluster model. The examined clusters were embedded in the simulated Coulomb fields that closely approximate the Madelung fields of the host surfaces. The adsorption properties of CO have been analyzed with reference to the basicity of the oxide support, bond order conservation energy, pairwise and non-pairwise additivity, associative adsorption, electrostatic potentials, and orbital interactions. CO adsorption on an oxide support is drastically enhanced when CO is adsorbed on a metal deposited on this support. A dramatic change is found, and explained, when one compares the CO binding energy to O~(2-) and F sites. The formation of a strong bond at the support-metal interface has a considerable consequence on the metal-CO binding energy. The binding of CO is dominated by the metal-CO pairwise additive term, and the non-additivity term increases with increasing the basicity of the support. While the classical contributions to the electrostatic interactions are quite similar for the deposited metals, they are quite dissimilar when going from defect-free to defect-containing surfaces. The adsorption properties correlate linearly with the basicity and energy gaps of the oxide support where the electrostatic potential generated by the oxide modifies the physical and chemical properties of the adsorbed metal and therefore its reactivity versus the CO adsorbate.