Catalytic properties of nano-brass clusters: A density functional theory study

Abstract

Brass (Cu-Zn) alloys are widely used as industrial materials. The structural and electronic properties of Cu-Zn clusters have been reported in theory recently [(Liu and Cheng, 2019); Journal of Cluster Science 2020, 31, 601–607], and the works have attracted intense research interest both experimentally and theoretically. However, to our knowledge the catalytic properties of the Cu-Zn clusters have not been analyzed. Here, we carry out our explorations of the catalytic properties of the selected Cu-Zn superatoms related to their geometric structures and stability. First, the global minimum structures of CuxZny (x + y = 14) alloy clusters are searched by an unbiased global method of genetic algorithm directly using the DFT functional. Among them, the spherical Cu8Zn6 and Cu10Zn4 satisfy magic numbers of the Jellium model and are two stable metal superatoms in this cluster series. Then, electrostatic potential surfaces of the brass clusters are analyzed, and the calculated results show that such alloy superatom has remarkable σ-holes with positive potential regions. Moreover, these electron-deficient regions can be considered as interaction sites with some Lewis bases. When a Lewis base CO gas molecule is attached to the alloy superatoms, we found that the CO bond distance become slightly elongated and its stretching frequency presents a significant red-shift. This is because that delocalized electrons of brass superatoms transfer towards the anti-bond π orbitals of CO molecule. Hence, these clusters may serve as potential catalysts for the covalent bond activation. However, the NH bond lengths of the clusters upon the NH3 adsorption are in accordance with that of the free NH3, and the analysis shows that the classical metals bind the NH3 molecule via donor interactions.