Molecular adsorption of NO on free-standing and on graphene-supported Mo₃W₅ cluster: a density functional theory investigation

The adsorption of molecular NO on the free-standing and graphene-supported Mo₃W₅ cluster is studied using methods from the gradient-corrected density functional theory. Before, the effect of the graphene support on the properties of the metal cluster was investigated. The interaction between the metal cluster and the graphene sheet takes place mainly through W atoms, which form up to three bonds with the support. Interaction energies are in the range from 0.6 to 1.5 eV. An amount of charge of about 0.4–0.5 e\(^-\) is transferred from the cluster to the support. Geometric distortions in the metal aggregate are negligible. An important decrease in the magnetic moment of Mo₃W₅ with respect to its free-standing value is observed after the interaction with the support. Molecular NO adsorbs on sites involving W atoms only, both for the free-standing and the supported metal cluster. Adsorption energies are in a range from 2 to 4 eV. A parallel mode is the preferred mode from an energetic point of view. Moreover, for that parallel adsorption mode, the N–O bond is more effectively activated. Magnetic moments change largely after adsorption indicating important rearrangement in the electronic configuration of the metal cluster. An important amount of electronic charge is transferred both from the free-standing and from the supported metal cluster to NO. The amount of charge transferred seems to be closely related to the activation of the N–O bond. The effect of the graphene sheet on the catalytic properties of Mo₃W₅ seems to be negligible, with the exception of some changes in the electronic configuration of the cluster.