To clarify the relationship between the type of the oxide support and the activity of the gold-doped oxide clusters toward H2 oxidation, a suitable closed-shell system AuV2O5+ is chosen to have a comparative study with AuCe2O4+, the first closed-shell cluster that is reactive toward H2 oxidation. The reaction of AuV2O5+ with H2 was characterized by mass spectrometry and density functional theory calculations. The AuV2O5+ cluster is reactive toward H2 leading to the major product of V2O5H2+ (+ Au), whereas the product of AuV2O4+ (+ H2O) is completely absent in the experiment. This is in sharp contrast with the similar reaction system of AuCe2O4+ with H2, in which the formation of H2O was experimentally evidenced. Theoretical calculations revealed that the distinct reaction behaviors between AuV2O5+ and AuCe2O4+ can be attributed to the gold–metal bond strength, which plays an important role in anchoring the gold atom. The weaker Au–V bond promotes the evaporation of Au, which has a negative effect on the total oxidation of H2 to H2O. This comparative study provides molecular-level mechanisms to understand the important roles of the gold–metal bond in the oxidation of hydrogen molecule over metal oxide supports.

Molecular clusters formed by m nitric acid molecules and n ammonia molecules are studied with density functional theory. For smaller clusters with m, n ≤ 4, all possible combinations of m and n are considered, while for larger clusters in the 5 ≤ m, n ≤ 8 range we only consider the possibilities with |m – n| ≤ 1. Hydrogen bond network formation is an important stabilization mechanism in these clusters. At the same time, proton transfer is generally preferred except in the smallest clusters. Nitric acid and ammonia evaporation rates of these clusters are calculated with both collision activation barriers and reaction thermodynamics explicitly considered. However, unlike in the case of cluster growth from sulfuric acid and ammonia, activation barriers do not play an important role here. If m and n are unequal, evaporation of the abundant species is always preferred. For clusters with m = n > 2, ammonia evaporation is faster than nitric acid. Stabilities of all clusters can be quantitatively evaluated by the evaporation rate of the preferred species. Larger clusters are generally more stable. However, exceptions can occur at structure motif transition point. Deviation from the stoichiometry of m = n significantly lowers the cluster stability. For a cluster pair formed by the same number of molecules, the nitric acid abundant one is more stable, which determines the growth pathway of these clusters.

The bonding properties between a single atom and its support have a close relationship with the stability and reactivity of single-atom catalysts. As a model system, the structural and electronic properties of bimetallic oxide clusters MV3Oyq (M = Au or Ag, q = 0, ±1, and y = 6–8) are systematically studied using density functional theory. The single noble metal atom Au or Ag tends to be adsorbed on the periphery of the V oxide clusters. Au prefers V sites for oxygen-poor clusters and O sites for oxygen-rich clusters, while Ag prefers O sites for most cases. According to natural population analysis, Au may possess positive or negative charges in the bimetallic oxide clusters, while Ag usually possesses positive charges. The bonding between Au and V has relatively high covalent character according to the bond order analysis. This work may provide some clues for understanding the bonding properties of single noble metal atoms on the support in practical single-atom catalysts, and serve as a starting point for further theoretical studies on the reaction mechanisms of related catalytic systems.

In this work, protonated and sodiated leucine-enkephalin (LE) were investigated by gas-phase hydrogen–deuterium exchange (HDX) performed on a linear ion trap time-of-flight mass spectrometer. It is found that more hydrogen atoms are exchanged in protonated LE than in sodiated LE, indicating the different conformations of the two peptide ions. To clarify further the experimental results, the conformations were calculated by using density functional theory, which shows that the terminal amino group is the most thermodynamically stable protonation site, while the sodium ion coordinated to four carbonyl oxygen atoms forms the most favourable sodium adduct. Limited HDX reactions of sodiated LE are explained by the rigid conformation and fewer exchangeable acidic hydrogen atoms from sodium coordination.

Reactions of vanadium oxide cluster cations with methane in a fast-flow reactor were investigated with a time-of-flight mass spectrometer. Hydrogen atom abstraction (HAA) reactions were identified over stoichiometric cluster cations (V2O5)N+ for N as large as 11, and the relative reactivity decreases as the cluster size increases. Density functional calculations were performed to study the structural, bonding, and electronic properties of the stoichiometric oxide clusters with the size N = 2–6. The geometric structures were obtained by means of topological and structural unit analyses together with global optimizations. Two types of oxygen-centered radicals were found in these clusters, which are active sites of the clusters in reactions with CH4. The size-dependent reactivity is rationalized by the charge, spin, and structural effects. This work is among the first reports that HAA from CH4 can take place on nanosized oxide clusters, which makes a bridge between the small reactive species and inert condensed phase materials for CH4 activation under low temperature.

The adsorption behaviour of a single O atom on Aunq clusters (n = 1–8, q = 0, ±1) was systematically investigated by DFT calculations. Both hybrid and pure GGA functionals (B3LYP and PBE) were used to provide reliable conclusions. The most stable structures of AunOq clusters were obtained by using global optimizations with a genetic algorithm. Cationic clusters tend to become three-dimensional for large clusters, as for Au8O+. The binding of O in AunOq clusters is quite strong, especially in the anionic clusters. The O atom can be bound to one, two, or three Au atoms, obtaining nearly one electron from gold atoms. Similarities have been found between AunOq and Aun+1q in terms of geometric structures and binding energies. Frontier molecular orbitals and the distribution of unpaired spin density on the O atom were discussed, both of which have a close relationship with the activity of the clusters.

The bonding properties between a single atom and its support have a close relationship with the stability and reactivity of single-atom catalysts. As a model system, the structural and electronic properties of bimetallic oxide clusters MV3Oyq (M = Au or Ag, q = 0, ±1, and y = 6–8) are systematically studied using density functional theory. The single noble metal atom Au or Ag tends to be adsorbed on the periphery of the V oxide clusters. Au prefers V sites for oxygen-poor clusters and O sites for oxygen-rich clusters, while Ag prefers O sites for most cases. According to natural population analysis, Au may possess positive or negative charges in the bimetallic oxide clusters, while Ag usually possesses positive charges. The bonding between Au and V has relatively high covalent character according to the bond order analysis. This work may provide some clues for understanding the bonding properties of single noble metal atoms on the support in practical single-atom catalysts, and serve as a starting point for further theoretical studies on the reaction mechanisms of related catalytic systems.

In this work, protonated and sodiated leucine-enkephalin (LE) were investigated by gas-phase hydrogen–deuterium exchange (HDX) performed on a linear ion trap time-of-flight mass spectrometer. It is found that more hydrogen atoms are exchanged in protonated LE than in sodiated LE, indicating the different conformations of the two peptide ions. To clarify further the experimental results, the conformations were calculated by using density functional theory, which shows that the terminal amino group is the most thermodynamically stable protonation site, while the sodium ion coordinated to four carbonyl oxygen atoms forms the most favourable sodium adduct. Limited HDX reactions of sodiated LE are explained by the rigid conformation and fewer exchangeable acidic hydrogen atoms from sodium coordination.