First-principles study of O2 activation on ligand-protected Au32 clusters

Poly(N-vinyl-2-pyrrolidone) (PVP) is often used to protect active Au clusters from coalescence. The influences of PVP on the O2 adsorption on Au32 clusters were investigated using density functional theory calculations. Various low-lying structures of O2:Au32 and O2:Au32:PVP complexes, in which the Au32 is either neutral or anionic and the O2 is either molecular or dissociative, were identified. The PVP influences were evaluated in terms of the changes in geometry, adsorption energy, charge redistribution, spin density, and density of states upon PVP pre-adsorption. Our calculations reveal that PVP weakly adsorbs on the cluster surface, with rather small changes in the structural, geometrical and electronic properties that are relevant to the O2 activation. The activity of neutral or anionic Au32 towards O2 is kept or slightly enhanced by PVP because of the cooperative adsorption of PVP and O2. This is the structural basis of choosing PVP as the protective ligand for Au clusters.