Reactions of Size-Selected Copper Cluster Cations and Anions with Nitric Oxide: Enhancement of Adsorption in Coadsorption with Oxygen

Abstract

Reactions of size-selected Cu(n)(±) and Cu(n)O(m)(±) (n = 3-19, m ≤ 9) clusters with NO were investigated in the near-thermal energy region under single collision conditions using a tandem-type mass spectrometer with two ion-guided cells. Oxygen atoms preadsorbed on the cluster can significantly enhance the NO adsorption probability and cause additional reactions. NO adsorption is observed particularly for anionic copper cluster dioxides, Cu(n)O2(-) (n ≥ 8), followed by the release of a Cu atom from Cu(n)O2(-) (n = 8, 10, and 12), which suggests that NO adsorbs strongly, i.e., dissociatively on these clusters. Density functional theory calculations support that dissociative adsorption of NO occurs in the reaction of Cu8O2(-) under the present experimental conditions. On the other hand, NO oxidation proceeds in reactions of oxygen-rich cluster cations such as Cu4O3(+), Cu6O5(+), Cu9O7(+), and Cu11O8(+).

NO Decomposition Activated by Preadsorption of O2 onto Copper Cluster Anions

“…Two product species, Cu 8 O 2 NO − and Cu 7 O 2 NO − , appear dominantly as described in our recent study. 13 Additionally, another peak is also observed at m/z ≈ 445, very slightly in Figure 1a and clearly in Figure 1b Figure 2). Furthermore, this assignment is supported by comparing the mass spectrum in Figure 1b with that measured in the CID experiment of Cu 8 O 2 − by Xe ( Figure 1c) because the intensity of the m/z = 445 peak in the multiple collision reactions with NO is considerably higher than that of Cu 7 − in Cu 8 O 2 − + Xe.…”

“…13 We found that the NO adsorption probabilities of copper cluster anions are dramatically enhanced by the preadsorption of two oxygen atoms in the size range of n ≥ 8. Furthermore, we observed that NO adsorption onto Cu n O 2 − (n = 8, 10, and 12) is followed by the release of a Cu atom.…”

“…16,17 The same computational method was successfully applied to our previous study on the adsorption and dissociation of an NO molecule on Cu 8 O 2 − . 13 Initially, the geometric structures of Cu 8 O 2 − were optimized with a doublet spin state, and three isomers were obtained. The vibrational frequency analysis confirmed that the lowest-energy isomer obtained represents a local minimum in energy because it has no imaginary vibrational frequency.…”

“…Similarly, neither Cu 10 − nor Cu 12 − react readily with an NO molecule. 13 However, Cu n O 2 − can adsorb NO molecules dissociatively to produce the anionic cluster tetroxides. Clearly, the activity of the anionic copper clusters contrasts with those of other transition metal clusters where the bare clusters are oxidized sequentially by NO molecules.…”

Stability of Aluminum-Doped Copper Cluster Cations and Their Reactivity toward NO and O2

“…23 Recently, we revealed that the preadsorption of seemingly harmful oxygen atoms onto copper cluster anions enhances the adsorption probability of NO and promotes the decomposition of NO. 22,24 This could be attributable to the contribution of 3d orbitals of the copper atoms. It is thus expected that the doping of p-or d-block metals such as aluminum or transition metals also affect the cluster reactivity drastically.…”