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The density functional theory (DFT) method has been used to investigate NO probe molecule adsorption on the stoichiometric (Mo16S32) and nonstoichiometric (Mo16S34and Mo16S29) clusters. The calculated adsorption energies indicate that the stoichiometric cluster has stronger NO affinity than the nonstoichiometric surfaces. It is also found that mononitrosyl adsorption is favored at low NO coverage, while dinitrosyl (germinal) and (NO)2dimer adsorption at high NO coverage are possible. Strong repulsive interaction has been found for the adsorbed dinitrosyl and (NO)2dimer species. In addition, the computed NO stretching frequencies for the mononitrosyl and dinitrosyl species agree well with the experimental data, while those of the dimer species are much lower than the suggested experimental data. [ABSTRACT FROM AUTHOR]

Density functional theory calculations have been carried out for CO adsorption on the Feoct2- and Fetet1-terminated Fe3O4(111) surfaces, which are considered as active catalysts in water-gas shift reaction. It is found that the on-top configurations are most stable on these two surfaces. Some bridge configurations are also stable in which the new C−O bond formed between the surface O atom and the C atom of CO. The adsorption on the Feoct2-termiated surface is more stable than on the Fetet1-terminated surface. The density of state reveals the binding mechanism of CO adsorption on the two surfaces. Our calculations have also shown that the absorbed CO can migrate from the on-top site to the bridge site or 3-fold site. The oxidation of CO via surface oxygen atoms is feasible, which is in good agreement with experimental results. [ABSTRACT FROM AUTHOR]