CO2 Adsorption over 3d Transition-Metal Nanoclusters Supported on Pyridinic N3-Doped Graphene: A DFT Investigation

CO₂ adsorption on bare 3d transition-metal nanoclusters and 3d transition-metal nanoclusters supported on pyridinic N₃-doped graphene (PNG) was investigated by employing the density functional theory. First, the interaction of Co₁₃ and Cu₁₃ with PNG was analyzed by spin densities, interaction energies, charge transfers, and HUMO-LUMO gaps. According to the interaction energies, the Co₁₃ nanocluster was adsorbed more efficiently than Cu₁₃ on the PNG. The charge transfer indicated that the Co₁₃ nanocluster donated more charges to the PNG nanoflake than the Cu₁₃ nanocluster. The HUMO-LUMO gap calculations showed that the PNG improved the chemical reactivity of both Co₁₃ and Cu₁₃ nanoclusters. When the CO₂ was adsorbed on the bare 3d transition-metal nanoclusters and 3d transition-metal nanoclusters supported on the PNG, it experienced a bond elongation and angle bending in both systems. In addition, the charge transfer from the nanoclusters to the CO₂ molecule was observed. This study proved that Co₁₃/PNG and Cu₁₃/PNG composites are adequate candidates for CO₂ adsorption and activation.

Co13O8—metalloxocubes: a new class of perovskite-like neutral clusters with cubic aromaticity

Exploring stable clusters to understand structural evolution from atoms to macroscopic matter and to construct new materials is interesting yet challenging in chemistry. Utilizing our newly developed deep-ultraviolet laser ionization mass spectrometry technique, here we observe the reactions of neutral cobalt clusters with oxygen and find a very stable cluster species of Co₁₃O₈ that dominates the mass distribution in the presence of a large flow rate of oxygen gas. The results of global-minimum structural search reveal a unique cubic structure and distinctive stability of the neutral Co₁₃O₈ cluster that forms a new class of metal oxides that we named as ‘metalloxocubes’. Thermodynamics and kinetics calculations illustrate the structural evolution from icosahedral Co₁₃ to the metalloxocube Co₁₃O₈ with decreased energy, enhanced stability and aromaticity. This class of neutral oxygen-passivated metal clusters may be an ideal candidate for genetic materials because of the cubic nature of the building blocks and the stability due to cubic aromaticity.

Theoretical study of the adsorption of hydrogen on cobalt clusters

Adsorption and dissociation of molecular hydrogen on transition metal clusters are basic processes of broad technological application in fields such as catalysis, hydrogenation reactions, hydrogen fuel cells, hydrogen storage, etc. Here we focus on two cobalt clusters, Co6 and Co13, and use the density functional formalism to investigate: (i) the mechanisms for adsorption and dissociation of hydrogen, and (ii) the competition between the two processes as the amount of hydrogen increases towards cluster saturation. The dissociative adsorption of hydrogen is the preferred adsorption channel for low coverage. Each individual H atom binds to the cluster with an ionic type of bonding, similar to that in metal hydrides. The electronic levels of the H atoms hybridize with the deepest levels of the Co cluster, leading to the stabilization of the system. In contrast H2 binds to the cluster with a weak covalent type of bond and the electronic density of the molecule becomes polarized. The electronic levels of the molecule are deeper than those of the Co cluster and do not hybridize with them, which explains the weak bonding of the molecule to the cluster. Interestingly, the high magnetic moments of the Co clusters do not change when H2 is adsorbed in molecular form, but the magnetic moments decrease by two Bohr magnetons upon dissociative adsorption of the molecule. Adsorption and dissociation of H2 on Co6 and Co13 exhibit similar features, although the adsorption energies on Co13 are stronger. Saturation of Co6 with hydrogen has been also investigated. Co6 can adsorb up to four H2 molecules in the dissociated form. Additional hydrogen is adsorbed in molecular form leading to a saturated cluster with sixteen hydrogen molecules, four dissociated and twelve molecular. This limit corresponds to a content of 8.4 wt% of hydrogen in the Co cluster, which is promising for the purpose of hydrogen storage.

Hydrogen storage in bimetallic Ti–Al sub-nanoclusters supported on graphene

Variations in the hydrogen gravimetric content of Ti and TiAl_n clusters supported on graphene layers.

Complex magnetic orders in small cobalt–benzene molecules

Organometallic clusters based on transition metal atoms are interesting because of their possible applications in spintronics and quantum information processing.