Support work function as a descriptor and predictor for the charge and morphology of deposited Au nanoparticles

Abstract

We show, using density functional theory calculations, that the charge, magnetic moment, and morphology of deposited Au nanoclusters can be tuned widely by doping the oxide support with aliovalent cations and anions. As model systems, we have considered Aun (n = 1, 2, or 20) deposited on doped MgO and MgO/Mo supports. The supports have been substitutionally doped with varying concentrations θ of F, Al, N, Na, or Li. At θ = 2.78%, by varying the dopant species, we are able to tune the charge of the Au monomer between −0.84e and +0.21e, the Au dimer between −0.87e and −0.16e, and, most interestingly, Au20 between −3.97e and +0.49e. These ranges can be further extended by varying θ. These changes in charge are correlated with changes in adsorption and/or cluster geometry and magnetic moment. We find that the work function Φ of the bare support is a good predictor and descriptor of both the geometry and charge of the deposited Au cluster; it can, therefore, be used to quickly estimate which dopant species and concentration can result in a desired cluster morphology and charge state. This is of interest as these parameters are known to significantly impact cluster reactivity, with positively or negatively charged clusters being preferred as catalysts for different chemical reactions. It is particularly noteworthy that the Na-doped and Li-doped supports succeed in making Au20 positively charged, given the high electronegativity of Au.