Adsorption of CO and NO molecules onto pentagonal clusters of aluminum: a DFT study

DFT calculations were carried out in order to determine the electronic and structural properties of pentagonal Al _n (I _h and D _5d symmetries), Al _n -CO, and Al _n -NO clusters, where n = 7, 13, 19, 43, or 55 atoms. As n was increased, the bare clusters were found to exhibit a transition in electronic behavior (from semiconductor to conductor) at n = 43 atoms. Clusters with a bound CO or NO molecule also showed this behavior, although their HOMO-LUMO energy gaps were smaller than those for the corresponding bare clusters. As the size of the Al _n -CO or Al _n -NO cluster increased, the presence of extra p electrons improved the capacity of the cluster to adsorb a CO or NO molecule and resulted in an increase in the electronic charge directed from the aluminum atom at the adsorption site to the adsorbed species (CO or NO), thus strengthening the Al-CO or Al-NO bond. Furthermore, the Al _n CO and Al _n NO clusters with n = 43 and 55 exhibited chemisorption, as did the Al₁₃-NO cluster; the other clusters presented physisorption, based on their adsorption energies. The tendency to adsorb either CO or NO increased with the size of the aluminum cluster. Graphical Abstract Adsorption of CO and NO molecules onto pentagonal clusters of aluminum: a DFT study.