On the Role of Alkali-Metal-Like Superatom Al12P in Reduction and Conversion of Carbon Dioxide

Developing efficient catalysts for the conversion of CO₂ into fuels and value-added chemicals is of great significance to relieve the growing energy crisis and global warming. With the assistance of DFT calculations, it was found that, different from Al₁₂X (X=Be, Al, and C), the alkali-metal-like superatom Al₁₂P prefers to combine with CO₂ via a bidentate double oxygen coordination, yielding a stable Al₁₂P(η²-O₂C) complex containing an activated radical anion of CO₂ (i.e., CO₂^.−). Thereby, this compound could not only participate in the subsequent cycloaddition reaction with propylene oxide but also initiate the radical reaction with hydrogen gas to form high-value chemicals, revealing that Al₁₂P can play an important role in catalyzing these conversion reactions. Considering that Al₁₂P has been produced in laboratory and is capable of absorbing visible light to drive the activation and transformation of CO₂, it is anticipated that this work could guide the discovery of additional superatom catalysts for CO₂ transformation and open up a new research field of superatom catalysis.     

First principles studies on the interaction of O2 with X@Al12 (X = Al−, P+, C,Si) clusters

The interaction of O₂ with the doped icosahedral X@Al₁₂ (X = Al^?, P⁺, C, Si) clusters with 40 valence electrons were investigated using density functional theory methods. A different behavior exhibited between Al₁₃^? and X@Al₁₂ (X = P⁺, C, Si) when they interact with O₂. The dissociation of O₂ on Al₁₃^? is strongly dependent on spin state of oxygen molecule. But X@Al₁₂ (X = P⁺, C, and Si) is not the case. The transform of spin moment from O₂ to Al₁₃^? is much faster. Small molecularly binding energy and relatively high energy barrier show that these clusters are all reluctant reacts with the ground state O₂. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010     

Theoretical study of isomerism of compounds of N2 and N2H2 molecules with aluminum clusters Al13 and Al12Ti

Segments of the potential energy surfaces corresponding to successive elementary stages of multistep fragmentation of nitrogen and diimine molecules upon their reaction with the aluminum cluster Al₁₃ and its doped analogue Al₁₂Ti have been calculated by the density functional theory method. The minimum energy pathways of these reactions have been calculated for the stages of physisorption, chemisorption, and N₂ and N₂H₂ fragmentation with different ways of insertion of fragments into the Al₁₃ and Al₁₂Ti cages. Relative energies, structural characteristics, and vibrational frequencies of coordinated and fragment isomers have been calculated, the barriers separating these isomers have been evaluated, and molecular diagrams of the reactions have been constructed. The effect of doping on the relative energies of intermediates and activation barriers has been considered. A conclusion has been drawn that doping with titanium should facilitate the reactions of molecular nitrogen with aluminum clusters. Unusual isomers with a five- and six-coordinate nitrogen atom N* have been localized. The results are compared with the data of analogous previous calculations of the PES of isomers corresponding to stepwise fragmentation of an acetylene molecule in related Al₁₃C₂H₂ and Al₁₂TiC₂H₂ derivatives.     

Single-point Attack of Two H2O Molecules towards a Lewis Acid Site on the GaAl12 Clusters for Hydrogen Evolution

The hydrogen evolution reaction (HER) of water with metallic aluminum-based materials provides an important way to address the global energy challenge; however, fundamental mechanism and reaction dynamics governing the chemical and electronic properties remain a debated research topic. Here we further study the HER mechanisms for water splitting on typical 13-atoms clusters, Al₁₂Ga and Al₁₃, by first-principles DFT calculations. We noted that the doping of a Ga atom into the Al₁₃ cluster could reduce the transition state barrier for H₂O dissociation on the metal cluster. Furthermore, it is interesting that the second water molecule prefers to adsorb on the same metal site giving rise to both thermodynamically and kinetically favorable reaction pathways. Based on the well-established complementary active sites (CAS) mechanism for metal cluster reactivity, we provide insights into the reaction dynamics of such metal clusters with two water molecules, which also sheds light on the Eley-Rideal and Langmuir-Hinshelwood mechanisms in surface science. Natural bond orbitals (NBO) analysis was conducted to evaluate the donor-acceptor charge-transfer interactions between the cluster and the nucleophilic reagent. These results gain a better understanding of the mechanism for water reacting with aluminum-based materials.     

A theoretical study of the effects of transition metal dopants on the adsorption and dissociation of hydrogen on nickel clusters

The structure, stability, adsorption, and dissociation of H₂ on nickel clusters doped with late transition metals were investigated using density functional theory with the BP86 functional. Molecular hydrogen physisorption occurred at a vertex atom with a low coordination number. Charge transfer between clusters and the H₂ molecule stabilized the physisorption. The chemisorption of H₂ occurred at the bridge sites, without any structural or spin change of the clusters. Among the pentamer clusters, Cd, Zn, and Au had the lowest chemisorption energies, while Ir and Pt had higher chemisorption energies for hydrogen. The computed reaction energies and activation barriers for the dissociation mechanism showed that dopants such as Rh, Pd, Pt, and Au have endothermic reaction energies and low activation barriers. This facilitates the reversible adsorption/dissociation of the H₂ molecule on these metal‐doped clusters. The dopant atoms play a major role in modulating the physisorption, chemisorption, and dissociation mechanism of H₂ on nickel clusters. © 2013 Wiley Periodicals, Inc.     

Stabilities of Al<Subscript>n</Subscript>Cu (n = 1–19) Clusters and Magnetic Properties of Three Cu-Doped Al Clusters

By using the Amsterdam Density Functional program, we have studied the geometric features, stabilities and magnetic properties of Al_nCu (n = 1–19) clusters. The magnetic structures of Al₁₇Cu₂ and Al₁₉Cu clusters are found. Although the high spin ground state of Al₁₂Cu cluster is in accordance with the Hund’s rule under spherical Jellium model (SJM), it is difficult to explain why the Al₁₇Cu₂ and Al₁₉Cu clusters exhibit larger magnetic moments by the model. A superatom model under equivalent charge distribution is proposed. The magnetic properties of the Cu-doped Al clusters can be explained well by combination of the superatom model with SJM.     

Study of Electronic,Optical Absorption and Emission in Pure and Metal‐Decorated Graphene Nanoribbons (C29H14‐X; X=Ni,Fe, Ti,Co+, Al+, Cu+): First Principles Calculations

Density functional theory (DFT) and time‐dependent density functional theory (TDDFT) calculations were performed with the basis sets 6‐31G for DFT and 6‐31G(d), 6‐31+G(d,p) for TDDFT on pure graphene nanoribbon (GNR) C₃₀H₁₄ and metal‐decorated C₂₉H₁₄‐X (MGNRs; X=Ni, Fe, Ti, Co⁺, Al⁺, and Cu⁺). The metal/carbon ratio (X:C 3.45 %) and the doping site were fixed. Electronic properties, that is, the dipole moment, binding energy, and HOMO–LUMO gaps, were calculated. The absorption and emission properties in the visible range (λ=400–720 nm) were determined. Optical gaps, absorption and emission wavelengths, oscillator strengths, and dominant transitions were calculated. Pure graphene was found to be the most stable form. However, of the MGNRs, C₂₉H₁₄?Co⁺ and C₂₉H₁₄?Al⁺ were found to be the most and least stable, respectively. All GNRs were found to have semiconducting nature. The optical absorption of pure graphene undergoes a shift on metal doping. Emission from the pure graphene followed Kasha′s rule, unlike the metal‐doped GNRs.     

Superatom-in-Superatom Nanoclusters: Synthesis,Structure, and Photoluminescence

We report a new strategy in which a thiolate-protected Ag₂₅ nanocluster can be doped with open d-shell group 8 (Ru, Os) and 9 (Ir) metals by forming metal hydride (RuH₂, OsH₂, IrH) superatoms with a closed d-shell. Structural analyses using various experimental and theoretical methods revealed that the Ag₂₅ nanoclusters were co-doped with the open d-shell metal and hydride species to produce superatom-in-superatom nanoclusters, establishing a novel superatom doping phenomenon for open d-shell metals. The synthesized superatom-in-superatom nanoclusters exhibited dopant-dependent photoluminescence (PL) properties. Comparative PL lifetime studies of the Ag₂₅ nanoclusters doped with 8–10 group metals revealed that both radiative and nonradiative processes were significantly dependent on the dopant. The former is strongly correlated with the electron affinity of the metal dopant, whereas the latter is governed predominantly by the kernel structure changed upon the doping of the metal hydride(s).     

Chlorine-passivated superatom Al<Subscript>37</Subscript> clusters for nonlinear optics

Utilizing a facile top-down synthetic procedure, here we report the finding of a chlorine-passivated Al₃₇ superatom cluster. It is demonstrated that the presence of electrophilic groups, severing as protecting ligands, alters the valence electron count of the metallic core and stabilize the as-prepared aluminum clusters especially when even-numbered chlorine atoms are located at equilibrium positions. Following the discussion regarding their reasonable stabilities, we illustrate the feasible reaction pathways in forming such chlorine-passivated Al₃₇ superatom clusters which bear delocalized superatomic orbitals with five valence 3P⁵ electrons shifting to the chlorine ligands indicative of a closed electron shell 2F¹⁴ of the metal core. The successful synthesis of such chlorine-protected aluminum clusters evidences the compatibility of general theory of cluster chemistry in both gas phase and wet chemistry. Such simple-ligand-protected aluminum clusters exhibit reverse-saturated-absorption (RSA) nonlinear optical property pertaining to electronic transitions within the discrete energy states of cluster materials.     

Adjusting magnetic moments of Sc13 and Y13 clusters by doping different X atom (X = Na,Mg, Al,Si, P)

We have investigated the structural and magnetic properties of the doped XM₁₂ and charged M₁₃ (X = Na, Mg, Al, Si, P; M = Sc, Y) clusters using the density‐functional theory with spin‐polarized generalized gradient approximation. It was found that doped atoms can induce significant change of the magnetic moments of Sc₁₃ and Y₁₃ clusters. The total magnetic moments of the NaM₁₂, MgM₁₂, AlM₁₂, SiM₁₂, and PM₁₂ clusters are regular 5, 6 (12), 7, 8, and 9 μ_b, respectively (but 19 μ_b for Sc₁₃ and Y₁₃, 12 μ_b for Y, 18 μ_b for Sc, Sc, and Y). The doped atom substituting the surface atom of the plausible icosahedral configuration is viewed as the ground‐state structure of the XM₁₂ (X = Na, P; M = Sc, Y) and MgSc₁₂ clusters. While for XM₁₂ (X = Al, Si; M = Sc, Y) and MgY₁₂ clusters, the doped atom occupying the central position of the icosahedral configuration is viewed as the ground‐state structure. The doping and the charging both enhance the stability of the Sc₁₃ and Y₁₃ clusters. These findings should have an important impact on the design of the adjustable magnetic moments systems. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Synthesis of Two‐Electron Bimetallic Cu–Ag and Cu–Au Clusters by using [Cu13(S2CNnBu2)6(C≡CPh)4]+ as a Template

Atomically precise Cu‐rich bimetallic superatom clusters have been synthesized by adopting a galvanic exchange strategy. [Cu@Cu₁₂(S₂CNⁿBu₂)₆(C≡CPh)₄][CuCl₂] ( 1 ) was used as a template to generate compositionally uniform clusters [M@Cu₁₂(S₂CNⁿBu₂)₆ (C≡CPh)₄][CuCl₂], where M=Ag ( 2 ), Au ( 3 ). Structures of 1 , 2 and 3 were determined by single crystal X‐ray diffraction and the results were supported by ESI‐MS. The anatomies of clusters 1 – 3 are very similar, with a centred cuboctahedral cationic core that is surrounded by six di‐butyldithiocarbamate (dtc) and four phenylacetylide ligands. The doped Ag and Au atoms were found to preferentially occupy the centre of the 13‐atom cuboctahedral core. Experimental and theoretical analyses of the synthesized clusters revealed that both Ag and Au doping result in significant changes in cluster stability, optical characteristics and enhancement in luminescence properties.     

Structures and electronic properties of Al7x0,- and Al13 X1,2,12- clusters with X=F, Cl, and Br

The structures, binding energies, and electronic properties for Al7X, Al7X-, Al13X-, Al13X2-, and Al13X12- (X = F, Cl, Br) were studied at the B3LYP/6-311+G(2d,p) level. Among the systems studied, Al7 and Al13 clusters in Al7X and Al13X- reveal alkali-like and halogen-like superatom characters, respectively. Al7 can bind with one halogen atom to form a salt-like compound as Al7+delta-X-delta. Al13- can combine with one halogen atom to form a diatomic halogen anion Al13X-. However, when adding more halogens, the superatom structure would be destroyed, resulting in low-symmetry compounds with the center Al atom moving toward the cluster surface. The structures of Al13X1,2,12- (X = F, Cl, Br) are similar to those of X = I; however, their binding energies and electron structures are much different. In addition, the analyses of the calculated NBO charges show that Cl and Br have similar properties, but much different from F, when interacting with the Al clusters. The Al-Cl and Al-Br bonds have more covalent character in Al7X and Al13X2,12-, in contrast to the corresponding Al-F bond, which has prominent ionic character.     

A Novel Concept for the Synthesis of Multiply Doped Gold Clusters [(M@AunM′m)Lk]q+

Heterometal‐doped gold clusters are poorly accessible through wet‐chemical approaches and main‐group‐metal‐ or early‐transition‐metal‐doped gold clusters are rare. Compounds [M(AuPMe₃)₁₁(AuCl)]³⁺ (M=Pt, Pd, Ni) ( 1 – 3 ), [Ni(AuPPh₃)_(8?2n)(AuCl)₃(AlCp*)_n] (n=1, 2) ( 4, 5 ), and [Mo(AuPMe₃)₈ (GaCl₂)₃(GaCl)]⁺ ( 6 ) were selectively obtained by the transmetalation of [M(M′Cp*)_n] (M=Mo, E=Ga, n=6; M=Pt, Pd, Ni, M′=Ga, Al, n=4) with [ClAuPR₃] (R=Me, Ph) and characterized by single‐crystal X‐ray diffraction and ESI mass spectrometry. DFT calculations were used to analyze the bonding situation. The transmetalation proved to be a powerful tool for the synthesis of heterometal‐doped gold clusters with a design rule based on the 18 valence electron count for the central metal atom M and in agreement with the unified superatom concept based on the jellium model.     

Iron Oxide Supported on Al2O3 Catalyst for Methane Decomposition Reaction: Effect of MgO Additive and Calcination Temperature

Production of hydrogen is a challenging task and have significant impact in the recent scenario. The alumina supported iron oxide nanoparticle synthesized using non‐ionic surfactant Triton‐X was found very effective for steady production of hydrogen through methane decomposition reaction. The high surface area, easily reducible catalyst calcined at 500 °C and 800 °C temperature showed steady activity towards methane decomposition reaction. At a higher reaction temperature there was catalyst deactivation. The doping of MgO facilitated particle growth rendering the poor catalytic activity. The TPR study showed that reducibility of TPR was difficult in presence of MgO additive. The formation of Fe? Mg? Al solid solution confirmed by XRD study was found mainly responsible for the lower catalytic activity. The bamboo‐shaped carbon nanotube formed from 20 % Fe/Al₂O₃ catalyst which is mainly because of the poor wetting property of quasi‐liquid metal and carbon nanotube.     

O2 dissociative adsorption on the Cu‐, Ag‐, and W‐doped Al(111) surfaces from DFT computation

The O₂ adsorption and dissociation on M‐doped (M = Cu, Ag, W) Al(111) surface were studied by density functional theory. The adsorption energy of adsorbate, the average binding energy and surface energy of Al surface, and the doping energy of doping atom were calculated. All the doped atoms can be stably combined with Al atoms, while being slightly embedded in the surface to a certain depth. The TOP‐type surfaces are the most stable doped surfaces for O₂ adsorption, which is related to the orbital hybridization between the adsorbate and the surface atoms, the electronegativity, and the orbital energy level of the doping atoms. Moreover, the O atoms and doping atoms contribute significantly to the density of states (DOS), especially the O‐p orbital electrons and the d orbital electrons of doping atoms. The degree of O₂ dissociation is related to the doping atoms on Al surfaces, and the doping atoms actually resist the dissociation of O₂. W atoms have the best resistance effect on the O₂ dissociation as compared with Cu and Ag atoms, especially W‐1NN surface, which has both large barrier energy and reaction energy.     

Magnetic Superatoms Based Spintronics: A DFT Study

A kind of magnetic superatom is designed by doping transition metal element into Na₈ clusters. Their electronic structure and spin-polarized transport properties are investigated using the first principles method. Our calculation shows that electrode materials have notable influence on the superatoms’ geometrical stability. Lithium lead is a good choice. Among all the superatoms, TiNa₈ and NiNa₈ give the highest transmission spin polarization (TSP), for negative and positive values, respectively. Relation between TSP and the magnetic moment of isolated superatom may lead to some promising designs in molecular spintronics devices.     

Finding all‐nonmetal transition‐metal‐like superatom and its magnetic building block

In novel superatom chemistry, it is very attractive that all‐metal clusters can mimic the behaviors of nonmetal atoms and simple nonmetal molecules. Wizardly all‐metal halogen‐like superatom Al₁₃ with 2P⁵ sub shell (corresponding to the 3p⁵ of chlorine) is the most typical example. In contrast, how to mimic the behaviors of magnetic transition‐metal atom using all‐nonmetal cluster is an intriguing challenge for superatom chemistry. In response to this based on human intuition, using quantum chemistry methods and extending jellium model from metal cluster to all‐nonmetal cluster, we have found out that all‐nonmetal octahedral B₆ cluster with characteristic jellium electron configuration 1S²1P⁶2S²1D⁸ in the triplet ground state can mimic the behaviors of transition‐metal Ni atom with electron configuration 3s²3p⁶4s²3d⁸ in electronic configuration, physics and chemistry. Interestingly, the characteristic order of 1S1P2S1D for the B₆ nonmetal cluster with short B‐B lengths is different from that of the traditional jellium model—1S1P1D2S for metal clusters with long M‐M lengths, which exhibits a novel size effect of nonmetal cluster on jellium orbital ordering. Based on the jellium electron configuration, the B₆ with the spin moment value of 2μ_B is a new all‐nonmetal transition‐metal nickel‐like superatom exhibiting a new kind of all‐nonmetal magnetic superatom. Finding the application of the all‐nonmetal magnetic superatom, we encapsulate the magnetic superatom B₆ inside fully hydrogenated fullerene forming a clathrate B₆@C₆₀H₆₀ with the spin moment value of 2μ_B. As the C₆₀H₆₀ cage as a polymerization unit can conserve the spin moment of endohedral B₆, the clathrate B₆@C₆₀H₆₀ is a new all‐nonmetal magnetic superatom building block. Naturally, magnetic superatom structures of the B₆ and B₆@C₆₀H₆₀ may be metastable.     

Structural Evolution and Superatoms in Molybdenum Atom Stabilized Boron Clusters: MoB<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n </Emphasis>= 10–24)

Doping transition metal atom is known as an effective approach to stabilize an atomic cluster and modify its structure and electronic properties. We herein report the effect of molybdenum doping on the structural evolution of medium-sized boron clusters. The lowest-energy structures of MoB_n (n?=?10, 12, 14, 16, 18, 20, 22, 24) clusters are globally searched using genetic algorithm combined with density functional theory calculations. We found that Mo doping has significantly affected the grow behaviors of B_n clusters, leading to a structural evolution from bowl-like to tubular and finally endohedral cage. The size-dependent binding energy, HOMO–LUMO gap, vertical ionization potential and vertical electron affinity show that MoB₁₂, MoB₂₂ and MoB₂₄ clusters have relatively higher stability and enhanced chemical inertness. More interestingly, the endohedral MoB₂₂ cage is identified as an elegant superatom, which satisfies 18-electron closed shell configuration well.     

Heteroatom‐doped MoSe2 Nanosheets with Enhanced Hydrogen Evolution Kinetics for Alkaline Water Splitting

Electrochemical water splitting for hydrogen generation is a vital part for the prospect of future energy systems, however, the practical utilization relies on the development of highly active and earth‐abundant catalysts to boost the energy conversion efficiency as well as reduce the cost. Molybdenum diselenide (MoSe₂) is a promising nonprecious metal‐based electrocatalyst for hydrogen evolution reaction (HER) in acidic media, but it exhibits inferior alkaline HER kinetics in great part due to the sluggish water adsorption/dissociation process. Herein, the alkaline HER kinetics of MoSe₂ is substantially accelerated by heteroatom doping with transition metal ions. Specifically, the Ni‐doped MoSe₂ nanosheets exhibit the most impressive catalytic activity in terms of lower overpotential and larger exchange current density. The density functional theory (DFT) calculation results reveal that Ni/Co doping plays a key role in facilitating water adsorption as well as optimizing hydrogen adsorption. The present work paves a new way to the development of low‐cost and efficient electrocatalysts towards alkaline HER.