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

The Reactivity of Ptn + Clusters With N2O Facilitated by Dual Lewis-Acid Sites

The size dependence of metal cluster reactions frequently reveals valuable information on the mechanism of nanometal catalysis. Here, the reactivity of the Ptn + (n = 1-40) clusters with N2O is studied and a significant dependence on the size of these clusters is noticed. Interestingly, the small Ptn + clusters like Pt3 + and Pt4 + are inclined to form N2O complexes; some larger clusters, such as Pt19 +, Pt21 +, and Pt23 +, appear to be unreactive; however, the others such as Pt3 , 9,15 + and Pt18 + are capable of decomposing N2O. While Pt9 + rapidly reacts with N2O to form a stable quasitetrahedron Pt9O+ product, Pt18 + experiences a series of N2O decompositions to produce Pt18O1-7 +. Utilizing high-precision theoretical calculations, it is shown how the atomic structures and active sites of Ptn + clusters play a vital role in determining their reactivity. Cooperative dual Lewis-acid sites (CDLAS) can be achieved on specific metal clusters like Pt18 +, rendering accelerated N2O decomposition via both N- and O-bonding on the neighboring Pt atoms. The influence of CDLAS on the size-dependent reaction of Pt clusters with N2O is illustrated, offering insights into cluster catalysis in reactions that include the donation of electron pairs.

Adsorption of Multiple NO Molecules on Anionic Gold Clusters: Electron Transfer and Disproportionation Enhanced by Molecular Aggregation

The reactions of Aun- clusters with multiple nitric oxide (NO) molecules are explored at 150 K by utilizing a mini-flow-tube reactor and a time-of-flight mass spectrometer. Adsorption of multiple NO molecules is observed on most Aun-, while disproportionation reactions only occur on even-sized Aun- with n = 4, 6, 8, 20 and odd-sized ones with n = 5 and 7. Theoretical calculations reveal the geometric structures and electronic states of the products containing bimolecular and trimolecular NO units, where two NO molecules typically form dimers. Different from NO monomers that weakly interact with odd-sized Aun- and form electron-sharing covalent bonds with Au10-(D3h) and Au16-, NO dimers can extract significant charge from parent Aun-. Regarding the three NO molecules, a predilection toward condensation into trimers on even-sized Aun- is observed, while the tendency is more toward an adsorption pattern of a dimer plus a monomer on odd-sized Aun-. The NO trimers register even higher charge gain from Aun- as compared with the NO dimers, which leads to an elevated degree of activation and induces the progression of disproportionation reactions. Therefore, when considering the reaction between NO and Aun-, it appears that NO has a propensity to form dimers or trimers on Aun-. This behavior of aggregate formation substantially enhances the ability of NO to absorb negative charges from Aun- although the occurrence of disproportionate dissociation reactions is initiated only for specific sizes.

Zooming in on the initial steps of catalytic NO reduction using metal clusters

The study of reactions relevant to heterogeneous catalysis on the surface of well-defined metal clusters with full control over the number of consituent atoms and elemental composition can lead to a detailed insight into the interactions between metal and reactants. We here review experimental and theoretical studies involving the adsorption of NO molecules on mostly rhodium-based clusters under near-thermal conditions in a molecular beam. We show how IR spectrosopic characterization can give information on the binding nature of NO to the clusters for at least the first three NO molecules. The complementary technique of thermal desorption spectrometry reveals at what temperatures multiple NO molecules on the cluster surface desorb or combine to form rhodium oxides followed by N₂ elimination. Variation of the cluster elemental composition can be a powerful method to identify how the propensity of the critical first step of NO dissociation can be increased. The testing of such concepts with atomic detail can be of great help in guiding the choices in rational catalyst design.

The study of reactions relevant to heterogeneous catalysis on metal clusters with full control over the number of constituent atoms and elemental composition can lead to a detailed insight into the interactions governing catalytic functionality.

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.

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.

NO disproportionation over defective 1T′-MoS2 monolayers

NO disproportionation can be catalyzed by MoS₂ monolayers loaded with S vacancies. When the MoS₂ sheet is under 3% compressive strain, two NO molecules at a S vacancy can form a NO₂. The left N atom will react with a third NO to afford N₂O under 3% tensile strain.