Atomic oxygen on silver is the crucial active species in many catalytic oxidation processes, while it is a big challenge to explore the relationship between its activity and molecular-level structures in condensed phases. We carried out kinetic measurements of the gas phase reactions between AgnO− (n = 1–8) and CO, in which the oxygen atoms were predicted to be terminal ones in AgO− and Ag2O−, in quasi-Ag–O–Ag chains for Ag3O− and Ag4O−, and on the two-fold or three-fold bridging positions in AgnO− (n = 5–8). All these oxygen species are highly reactive even at a low temperature of 150 K. AgnO− (n = 1, 2, 5–8) with terminal or bridging oxygen generate free CO2, while the quasi-chains of AgnO− (n = 3, 4) generate chemically bonded CO2 with a structural formula of Agn–CO2–Ag2− (n = 1, 2). Density functional theory calculations well interpreted all experimental observations, showing that no extra excitation energies are needed to initiate all these reactions. The structurally dependent mechanisms and the formation of chemically bonded CO2 revealed in this work help us to catch a glimpse of some important processes and intermediates on real silver catalysts.

The adsorption and activation of NO on microsilver species provide the foundation to understand the mechanism of NO removing reactions on silver based catalysts. However, the diversiform of the geometrical structures and electronic properties of microsilver species in condensed phases has posed considerable challenges for exploring these interactions. We study the reactions of NO with bare silver clusters Agn± (7–69) in the gas phase using a continuous flow reactor running at low temperatures. Evidence for NO unit adsorption, the formation of (NO)2 and the reduction of NO is observed on different cluster sizes. The kinetic rates of initial NO unit adsorption are closely related to silver clusters' global electronic properties. The low electron binding energy and the unpaired electron of a silver cluster favor the adsorption and activation of NO. In particular, the clusters with one less electron than those of closing electron shells are generally inert and the sizes having one more electron outside these shells are generally quite reactive. These observations depict a general figure of interactions between NO and microsilver species, in which electron transfer from silver to NO dominates.

Exploring the reactivity of metal clusters is an important task in cluster science, while only a few previous studies involve the reactions of nano-sized ones. Here we report a kinetic measurement on reactions of Agn− (n = 6–69) with O2 using a flow reactor running at 120 K. Their relative rates were obtained by fitting decay processes of parent ions at different O2 flow rates. Comparing the variations of the kinetic rates and the photodetachment energies of Agn− (i.e. the binding energies of their excess electrons), we distinguished the separate effect of clusters' spins or their electron binding strength. This work firstly shows that reactions of O2 and Agn− up to nano sizes are still dominated by the clusters' global electronic properties. This conclusion is conceptually important for understanding the reaction mechanisms on silver based nanocatalysts.

The low lying structures of Aun(CO)+ (n = 1–10) within 1.0 eV from their global minima were explored using a structure searching program (Atomic Global Minimum Locator) and density functional theory (DFT) calculations. According to general chemical intuitions, CO should prefer to stay on the lowest coordination sites of gold frames. However, our calculations showed that this preference becomes very weak in large Aun(CO)+, and even negligible for their compact three dimensional structures. This character relates to the intrinsic fluxionality of gold cluster frames, which apparently readjust their bond parameters after CO adsorption. The stretching frequency of a terminal-bonded CO decreases with increasing cluster size, and structural details of the adsorption sites have insignificant influences. The bridge-bonded COs, on the contrary, has far low stretching frequencies mainly determined by structural details of the two bridge sites. The frequency variation of CO relates to the electron donation and back-donation between gold and CO. Since all the above regularities on the adsorption and frequency of CO were summarized from large amount of low lying structures rather than some specific ones, they can be used to understand adsorption of CO on active sites of real gold catalysts, whose structures are diversiform and usually unclear.

Conversion of NO to other nitrogen oxides is an elementary step in its catalytic removal processes. On coinage metal surfaces, two kinds of NO activation mechanisms have been well documented: the unimolecular dissociation of NO generates two adsorbed atoms, and the dissociation of an adsorbed (NO)2 unit generates an adsorbed O and a free N2O. In this work, we observed a disproportionation mechanism involving three NO molecules on Au6– at a very low temperature (150 K), in which an adsorbed (NO)2 reacts with a free NO forming an adsorbed NO2 and a free N2O. The density functional theory (DFT) calculations indicated that this disproportionation step is significantly exothermic and has a very low activation barrier. The charge distributions on the involved cluster complexes and the correlation between the activity and the electronic properties of Au6– indicate the important role of extra negative charge in all reaction steps. The disproportionation mechanism revealed in this work could possibly exist in the NO removal processes on real gold catalysts.

•We obtained IR photodissociation spectra of MO(CO)5+ (M = Sc, Y, La and Ce) in the gas phase.•We studied the structures of MO(CO)5+ (M = Sc, Y, La and Ce) using DFT calculations.•The dominant structures of MO(CO)5+ (M = Sc, Y, La and Ce) have C5v geometry.The MO(CO)5+ (M = Sc, Y, La and Ce) complexes are generated and analyzed using an infrared photodissociation spectrometer. Their CO stretching frequencies are determined to be 2210 cm−1, 2206 cm−1, 2198 cm−1 and 2196 cm−1 for M = Sc, Y, La and Ce, respectively. The simulated spectra from DFT calculations are compared with the experimental results, indicating MO(CO)5+ (M = Sc, Y, La and Ce) are or very close to pentagonal pyramidal structures with C5V symmetry. The comparisons of these complexes with other metal carbonyls help to elucidate the characteristics of CO coordination in various metal species.

•Saturated adsorption of CO on Aun+ measured by mass spectrometry.•Abrupt changes in CO adsorption after coadsorption of single H2O is observed.•CO adsorption rate on Au6+ increases ten fold in the presence of water vapor.•DFT calculations reveal the presence of dynamic fluxionality that explains data.•Binding energy calculations explain absence of adsorbed H2O in final CO complex.This paper presents mass spectrometry measurements of the saturated adsorption of CO in the presence of coadsorbed H2O on gas phase gold cluster cations, Aun+, n = 3–20, stored in a quadrupole ion trap. Initial mass spectra obtained at 150 K for specific cluster ion sizes as a function of CO pressure and reaction time, indicate increased CO saturation levels correlated with the coadsorption of background H2O vapor. Subsequent to these low temperature experiments, measurements were made of CO and H2O coadsorbed on Au6+ as a function of reaction time at 300 K. These mass spectra indicate that the reaction rate at constant CO pressure increases by an order of magnitude for a constant H2O pressure. First-principles density-functional theory calculations in conjunction with the above measurements allowed identification of energy barriers that control dynamic structural fluxionality between adsorption complexes that depends strongly on preadsorbed water. The calculations revealed that in the presence of H2O the energy barrier for the transition state between ground-state triangular and the incomplete hexagonal isomers of the [Au6(CO)3(H2O)2]+ complex is reduced to ∼0 eV and the exothermicity is increased by 0.43 eV. The theoretical results also identified kinetic pathways exhibiting a transition of the incomplete hexagonal isomer of [Au6(ih)(CO)3(H2O)2]+ to the final saturated complex, Au6(ih)(CO)4+. The energetics and kinetic pathway calculations are consistent with increased formation rates of Au6(CO)4+ as observed in mass spectra. The insights gained from these theoretical results not only explain measurements of the CO saturated adsorption on Au6+ in the presence of water, but also assist in rationalizing coadsorption results obtained over the broader range of cluster size at 150 K.

Laser-ablated magnesium species were codeposited with SO2 in excess argon or neon on the substrate at 4 K. The reactions mainly produced Mg(η2-O2S), Mg(η2-O2S)2, Mg2(η2-O2S), OMg2(η2-SO), and Mg(η2-SO) complexes, which were identified by isotopic substitutions and density functional frequency calculations (B3LYP and BPW91). In addition, the collected infrared spectra suggest that the single Mg atoms could react with SO2 to form the Mg(η2-O2S) complex on annealing, which further reacts with SO2 to produce the Mg(η2-O2S)2 complex on irradiation. In contrast, the reactions of magnesium dimers lead to cleavage of the S═O bond in SO2 on irradiating. Structural and bonding characteristics of these generated complexes, which shed light on the different performances of single Mg atom and its dimer in their reactions with small molecules, are discussed.

The octacoordinate metal carbonyls La(CO)8+ and Ce(CO)8+ were observed in laser vaporization of La and Ce in pure CO gas. The peak intensities in the mass spectra, the infrared photodissociation spectra, and the theoretical calculations indicate that all CO ligands in these two complexes are bonded with the central metal atoms. The CO stretching frequencies in La(CO)8+ and Ce(CO)8+ are determined to be 2110 and 2108 cm–1, respectively. Theoretical studies indicate that the most stable structures for La(CO)8+ and Ce(CO)8+ are an Oh geometry at its triplet state and a slightly distorted Oh geometry at its quartet state, respectively. These two complexes represent new octacoordinate metal carbonyls after previously determined U(CO)8+ and Y(CO)8+.

Atomic oxygen on silver is the crucial active species in many catalytic oxidation processes, while it is a big challenge to explore the relationship between its activity and molecular-level structures in condensed phases. We carried out kinetic measurements of the gas phase reactions between AgnO− (n = 1–8) and CO, in which the oxygen atoms were predicted to be terminal ones in AgO− and Ag2O−, in quasi-Ag–O–Ag chains for Ag3O− and Ag4O−, and on the two-fold or three-fold bridging positions in AgnO− (n = 5–8). All these oxygen species are highly reactive even at a low temperature of 150 K. AgnO− (n = 1, 2, 5–8) with terminal or bridging oxygen generate free CO2, while the quasi-chains of AgnO− (n = 3, 4) generate chemically bonded CO2 with a structural formula of Agn–CO2–Ag2− (n = 1, 2). Density functional theory calculations well interpreted all experimental observations, showing that no extra excitation energies are needed to initiate all these reactions. The structurally dependent mechanisms and the formation of chemically bonded CO2 revealed in this work help us to catch a glimpse of some important processes and intermediates on real silver catalysts.

Exploring the reactivity of metal clusters is an important task in cluster science, while only a few previous studies involve the reactions of nano-sized ones. Here we report a kinetic measurement on reactions of Agn− (n = 6–69) with O2 using a flow reactor running at 120 K. Their relative rates were obtained by fitting decay processes of parent ions at different O2 flow rates. Comparing the variations of the kinetic rates and the photodetachment energies of Agn− (i.e. the binding energies of their excess electrons), we distinguished the separate effect of clusters' spins or their electron binding strength. This work firstly shows that reactions of O2 and Agn− up to nano sizes are still dominated by the clusters' global electronic properties. This conclusion is conceptually important for understanding the reaction mechanisms on silver based nanocatalysts.

The adsorption and activation of NO on microsilver species provide the foundation to understand the mechanism of NO removing reactions on silver based catalysts. However, the diversiform of the geometrical structures and electronic properties of microsilver species in condensed phases has posed considerable challenges for exploring these interactions. We study the reactions of NO with bare silver clusters Agn± (7–69) in the gas phase using a continuous flow reactor running at low temperatures. Evidence for NO unit adsorption, the formation of (NO)2 and the reduction of NO is observed on different cluster sizes. The kinetic rates of initial NO unit adsorption are closely related to silver clusters' global electronic properties. The low electron binding energy and the unpaired electron of a silver cluster favor the adsorption and activation of NO. In particular, the clusters with one less electron than those of closing electron shells are generally inert and the sizes having one more electron outside these shells are generally quite reactive. These observations depict a general figure of interactions between NO and microsilver species, in which electron transfer from silver to NO dominates.