Theoretical study of NH₃, H₂S, and HCN adsorption enhancement on defective graphene-supported Cu₁₉ clusters

Recent studies have shown that graphene-supported metal clusters can enhance catalytic reactivity compared with corresponding metal clusters. In this study, the adsorptions of NH3, H2S, and HCN on Cu-19 and defective graphene-supported Cu-19 clusters are investigated using plane-wave density functional theory. The results reveal the three gas molecules can be adsorbed on three types of top sites of Cu atoms, respectively. The adsorption energies of the corresponding adsorption sites on the defective graphene-supported Cu-19 clusters are all increased compared with those on the Cu-19 clusters. The orbital-resolved, crystal orbital Hamilton population analysis demonstrates that the larger the integrated crystal orbital Hamilton population, the stronger the adsorption between the gas molecule and the bonded Cu atom. The center of antibonding states on the defective graphene-supported Cu-19 is shifted upward relative to Fermi level compared to the corresponding one on pure Cu-19, which explains the enhanced adsorption energy on defective graphene-supported Cu-19. In addition, the closer d-band center to the Fermi level on the defective graphene-supported Cu-19 indicates a stronger adsorption capacity than on pure Cu-19.