Reduction of nitrogen oxides (NO ) by superalkalis

Interaction of N2, O2 and H2 Molecules with Superalkalis

Superalkalis (SAs) are exotic clusters having lower ionization energy than alkali atoms, which makes them strong reducing agents. In the quest for the reduction of diatomic molecules (X2) such as N2, O2, and H2 using Møller-Plesset perturbation theory (MP2), we have studied their interaction with typical superalkalis such as FLi2, OLi3, and NLi4 and calculated various parameters of the resulting SA-X2 complexes. We noticed that the SA-O2 complex and its isomers possess strong ionic interaction, which leads to the reduction of O2 to O2 - anion. On the contrary, there are both ionic and covalent interactions in SA-N2 complexes such that the lowest energy isomers are covalently bonded with no charge transfer from SA. Further, the interaction between SA and H2 leads to weakly bound complexes, which results in the adsorption of H2 molecules. The nature of interaction is found to be closely related to the electron affinity of diatomic molecules. These findings might be useful in the study of the activation, reduction, and adsorption of small molecules, which can be further explored for their possible applications.

Superalkalis with Hydrogen as Central Electronegative Atom and their Possible Applications: Ab Initio and DFT Study

Superalkalis are unusual species having ionization energies lower than that of the alkali metals. These species with various applications are of great importance in chemistry due to their low ionization energies and strong reducing property. A typical superalkali contains a central electronegative core decorated with excess metal ligands. In the quest for novel superalkalis, we have designed the superalkalis HLi2, HLiNa and HNa2 using hydrogen as central electronegative atom for the first time employing high level ab initio (CCSD(T), MP2) and density functional theory (ωB97X-D) methods. The superalkalis exhibit very low ionization energies, even lower than that of cesium. Stability of these species is verified from binding energy and dissociation energy values. The superalkalis are capable of reducing SO2, NO, CO2, CO and N2 molecules by forming stable ionic complexes and therefore can be used as catalysts for the reduction or activation of systems possessing very low electron affinities. The superalkalis form stable supersalts with tailored properties when interact with a superhalogen. They also show remarkably high non-linear optical responses, hence could have industrial applications. It is hoped that this work will enrich the superalkali family and spur further theoretical and experimental research in this direction.

DFT and QTAIM studies on the reduction of carbon monoxide by superalkalis

Carbon monoxide (CO) is a toxic gas molecule with no positive electron affinity, which makes it difficult to reduce it into CO¯. In this work, we perform density functional theory (DFT) and quantum theory of atoms in molecule (QTAIM) based studies on the interaction of CO molecule with superalkali (SA) clusters. Our findings suggest that this interaction results in SA(CO) complexes, which are stabilized by purely ionic as well as partially covalent bonds although their binding energy decreases with the increase in the size of SA clusters. In these ionic complexes, the electron is transferred from the SA cluster to the CO molecule. This suggests the single-electron reduction of the CO molecule by interacting with superalkalis. This work may offer some novel insights into the detection and reduction of stable CO molecule and related systems.

Reducing Properties of Superalkalis on Pyridinic Graphene Surfaces: a Computational Study

The hyperlithiated species Li k + 1 F k (k=1, 2, 3, and 4) have been studied by quantum mechanical (QM) methods. Different structures have been localized for each molecule by the CBS-QB3 composite method: all the isomers show superalkali properties and strong tendency to donate an electron to carbon dioxide forming stable Li k + 1 F k · · · CO 2 complexes. With the aim to find molecular systems able to stabilize superalkalis, geometries of complexes between superalkalis and pyridine and superalkalis and graphene surfaces doped with a pyridinic vacancy were calculated. The pyridinic graphene sheets were modeled with two finite molecular systems C₆₉ H₂₁ N₃ and C₁₁₇ H₂₇ N₃ . The interaction with one pyridine molecule is quite weak and the superalkali maintains its structure and electron properties. The affinity for graphene sheets is instead stronger and the superalkalis tend to deform their geometry to better interact with the graphene surface. However, the superalkalis continue to show the tendency to transfer electrons to carbon dioxide reducing CO₂ , as found in graphene absence.

Recent Progress on the Design, Characterization, and Application of Superalkalis

Superalkalis are clusters or molecules featuring lower ionization energies (IEs) than that of cesium atoms, and thus exhibit excellent reducing properties. Such special species have great potential to be used in the synthesis of unusual charge-transfer salts and cluster-assembled nanomaterials with tailored properties, in the reduction of carbon dioxide, or as hydrogen storage materials and noble-gas-trapping agents, etc. In this regard, ongoing efforts have been devoted to designing and characterizing superalkalis of new types. The recent progress on the study of superalkalis in terms of theoretical design, characterization, and potential application is summarized in this minireview. We hope this review will not only provide a broad overview of this research field, but also highlight the prospect of further extending the experimental synthesis and practical application of superalkalis.