Stability and Reversible Oxidation of Sub-Nanometric Cu-5 Metal Clusters: Integrated Experimental Study and Theoretical Modeling

Sub-nanometer metal clusters have special physical and chemical properties, significantly different from those of nanoparticles. However, there is a major concern about their thermal stability and susceptibility to oxidation. In situ X-ray Absorption spectroscopy and Near Ambient Pressure X-ray Photoelectron spectroscopy results reveal that supported Cu-5 clusters are resistant to irreversible oxidation at least up to 773 K, even in the presence of 0.15 mbar of oxygen. These experimental findings can be formally described by a theoretical model which combines dispersion-corrected DFT and first principles thermochemistry revealing that most of the adsorbed O-2 molecules are transformed into superoxo and peroxo species by an interplay of collective charge transfer within the network of Cu atoms and large amplitude breathing motions. A chemical phase diagram for Cu oxidation states of the Cu-5-oxygen system is presented, clearly different from the already known bulk and nano-structured chemistry of Cu.

Automated summary

This study investigates the thermal stability and oxidation susceptibility of sub-nanometer metal clusters. The experimental results show that Cu-5 clusters supported on a substrate can resist irreversible oxidation up to at least 773 K, even in the presence of 0.15 mbar of oxygen. Theoretical calculations based on dispersion-corrected density functional theory and first principles thermochemistry explain the transformation of adsorbed O-2 molecules into superoxo and peroxo species through collective charge transfer and large amplitude breathing motions within the network of Cu atoms. A chemical phase diagram for Cu oxidation states in the Cu-5-oxygen system is presented, revealing distinct chemistry compared to bulk and nano-structured Cu.