Adsorption of the Ir4 cluster on single-wall carbon nanotubes: the zigzag types are more suitable

Abstract

Density functional calculations have been performed to investigate the adsorption of the Ir₄ cluster on different SWNTs. We find that the tetrahedral isomer adsorbed on the studied tubes, with a triangular face on the SWNT, is predominantly favored. The metal–SWNT interaction in the zigzag tube-supported Ir₄ systems is significantly stronger than that in the armchair-supported systems. A strong hybridization between the p orbital of the SWNT and the d orbital of the Ir atoms is formed when the Ir₄ cluster is adsorbed on the SWNT surface. The charge density difference also shows that a substantial concentration of electrons accumulates as Ir–C bonds. The CO/NO adsorption on the SWNT-supported Ir₄ cluster is also investigated. All of the zigzag tube-supported Ir₄ clusters possess lower adsorption energies relative to the free- and armchair-supported Ir₄ clusters. Our investigation indicates that the zigzag-type SWNTs not only stabilize the Ir clusters, but also enhance their catalytic performance.