Quantifying the Impact of Relativity and of Dispersion Interactions on the Activation of Molecular Oxygen Promoted by Noble Metal Nanoparticles

We compared the mechanism of O-2 dissociation catalyzed by Cu-38, Ag-38, and Au-38 nanoparticles. Overall, our results indicate that O-2 dissociation is extremely easy on Cu-38, with an almost negligible barrier for the O-O breaking step. It presents an energy barrier close to 20 kcal/mol on Ag-38, which decreases to slightly more than 10 kcal/mol on Au-38. This behavior is analyzed to quantify the impact of relativity and of dispersion interactions through a comparison of nonrelativistic, scalar-relativistic, and dispersion-corrected DFT methods. Nonrelativistic calculations show a clear trend down the triad, with larger in size nanoparticle (NP), weaker O-2 adsorption energy, and higher O-2 dissociation barrier, which is so high for Au-38 to be in sharp contrast with the mild conditions used experimentally. Inclusion of relativity has no impact on the O-2 adsorption energy, but it reduces the energy barrier for O-2 dissociation on Au-38 from 30.1 to 11.4 kcal/mol, making it even lower than that on Ag-38 and consistent with the mild conditions used experimentally. Dispersion interactions have a remarkable role in improving the adsorption ability of O-2 on the heavier Ag-38 and especially Au-38 NPs, contributing roughly 50% of the total adsorption energy, while they have much less impact on O-2 adsorption on Cu-38