Infrared spectroscopic and theoretical studies on the formation of Au2NO− and AunNO (n=2–5) in solid argon

Various Bond Interactions between NO and Anionic Gold Clusters: A Theoretical Calculation

We studied the electronic and geometrical structures of AunNO- (n = 1-20) using the B3LYP method with relatively large basis sets to understand the size dependent reactivities of Aun- with...

Structures of Nitrogen Oxides Attached to Anionic Gold Clusters Au4- Revealed by Infrared Multiple Photon Dissociation Spectroscopy

The adsorption forms of NO and NO₂ on anionic Au₄^- clusters were investigated by a combination of IR multiple photon dissociation (IRMPD) spectroscopy and density functional theory (DFT) calculations. For all three species investigated (Au₄NO^-, Au₄N₂O₂^-, and Au₄NO₂^-), the spectra were found to be consistent with a Y-shaped Au₄^- cluster with triangular Au₃ and one Au atom sticking out, on which NO and NO₂ molecules adsorb molecularly. These species are considered as intermediates of the Au₄^--mediated disproportionation reaction of NO, Au₄(NO)₃^- → Au₄(NO₂)(N₂O)^-. We discuss the reaction path on the basis of the found geometries and energies and conclude that the disproportionation reaction of NO can occur catalytically on the Au₄^- cluster.

Reaction of nitric oxide molecules on transition-metal-doped silver cluster cations: size- and dopant-dependent reaction pathways

We report size- and dopant-dependent reaction pathways as well as reactivity of gas-phase free Ag_nM⁺ (M = Sc-Ni) clusters interacting with NO. The reactivity of Ag_nM⁺, except for M = Cr and Mn, exhibits a minimum at a specific size, where the cluster cation possesses 18 or 20 valence electrons consisting of Ag 5s and dopant's 3d and 4s. The product ions range from NO adducts, Ag_nM(NO)_m⁺, and oxygen adducts, Ag_nMO_m⁺, to NO₂ adducts, Ag_nM(NO₂)_m⁺. At small sizes, Ag_nMO_m⁺ are the major products for M = Sc-V, whereas Ag_nM(NO)_m⁺ dominate the products for M = Cr-Ni in striking contrast. In both cases, these reaction products are reminiscent of those from an atomic transition metal. However, the reaction pathways are different at least for M = Sc and Ti; kinetics measurements reveal that the present oxygen adducts are formed via NO adducts, while, for example, Ti⁺ is known to produce TiO⁺ directly by reaction with a single NO molecule. At larger sizes, on the other hand, Ag_nM(NO₂)_m⁺ are dominantly produced regardless of the dopant element because the dopant atom is encapsulated by the Ag host; the NO₂ formation on the cluster is similar to that reported for undoped Ag_n⁺.

Adsorption and reactions of NO molecules on anionic gold clusters in the size range below 1 nm: effects of clusters' global electronic properties

We systemically studied adsorption and reactions of NO on Au_n^- (n≤ 80) using a mini flow-tube reactor running at 150 K. For Au_n^- (n≤ 11), their reactions with NO mainly formed cluster complexes containing various numbers of NO units; for Au_n^- (n≥ 12), most active sizes eventually formed specific complexes Au_n(NO)₃^-. The relative rates of the reactions with the first NO were measured. Correlations between these relative rates and the adiabatic detachment energies (ADEs) of Au_n^- revealed the dominant effect of the clusters' spins and a more complicated electron transfer mechanism than that of reactions with O₂. Au₂₀^- as well as previously reported Au_4,6,8^- is an exceptional size, which eventually formed the disproportionate product Au₂₀NO₂^-, and all these four sizes have very low ADEs. The effects of the clusters' global electronic properties on adsorption and reactions of NO on anionic gold are helpful to understand catalytic mechanisms of gold-based catalysts in NO removal reactions.

Low-Temperature Disproportionation Reaction of NO on Au6-: A Mechanism Involving Three NO Molecules Promoted by the Negative Charge

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.

The adsorption and activation of NO on silver clusters with sizes up to one nanometer: interactions dominated by electron transfer from silver to NO

Evidence for NO unitary adsorption, the formation of (NO)₂ and the reduction to form N₂O is observed on silver clusters with sizes up to one nanometer. The adsorption and activation of NO are enhanced by electron transfer from silver to NO.

The role of atomic excited states of Au on N2O capture and activation: a multireference second-order perturbation theory study

Nitrous oxide (N(2)O) is an intermediate compound formed during catalysis occurring in automobile exhaust pipes. Atomic Au in its ground state is unable to react with N(2)O, however, several Au excited states are bound to N(2)O, but not all of these states are able to activate N(2)O bonds. In this work, N(2)O capture and activation by a single Au atom are studied considering Au in the ground and excited states with multiplicities = 2, 4 and 6. The Au + N(2)O reactions are studied at multireference second-order perturbation level of theory using C(s) symmetry. The AuN(2)O ((4)A', (4)A'', (6)A' and (6)A'') adducts are spontaneously created from Au excited states. From these complexes, only the (4)A', (6)A' and (6)A'' states exhibit N(2)O activation reaction paths yielding N(2,) NO and O atoms as end products when N(2)O approaches Au excited states side-on. Cations both ground and excited states, capture N(2)O although only the Au(+) ((5)A') + N(2)O ((1)Σ(+)) → NAuNO(+) ((5)A') reaction (for the end-on and side-on approaches) shows N(2)O activation with N-N bond breaking. In the case of Au anions, the ground state and most of the excited states capture N(2)O and activation takes place according to Au(-) ((3)A', (5)A', (5)A'') + N(2)O ((1)Σ(+)) → AuO(-) ((3)A', (5)A', (5)A'') + N(2)(g) for the N(2)O end-on approach by the oxygen atom. The reaction paths show a metal-gas dative covalent bonding character. Mulliken charge population analysis obtained for the active states shows that the binding is done through charge donation and retro-donation between the metal and the N(2)O molecule.