Reaction of tungsten anion clusters with molecular and atomic nitrogen

Abstract

Ultraviolet photoelectron spectra for W n N 2 Ϫ (nϭ1 -8) clusters produced by addition of atomic and molecular nitrogen on W anion clusters are presented. Evidence is provided that molecular chemisorption of N 2 is more stable than the dissociative one on tungsten anion clusters consisting of eight atoms or less, which is completely different from the results on tungsten bulk surfaces. A general tendency toward molecular chemisorption for small clusters can be explained by reduced charge transfer from the metallic d-orbitals of cluster in contrast to bulk d-orbitals. Comparative studies on chemisorption of atomic and molecular species of diatomic molecules on nanoclusters are expected to provide important information on size-dependent changes of chemical properties of nanoclusters.

Theoretical study of molecular nitrogen adsorption on Wn clusters

“…Neutral W n clusters with n < 15 show relatively low reactivity towards nitrogen adsorption, whereas a sharp jump of the reactivity is detected for n = 15 at liquid-nitrogen temperature as well as room temperature [14,15]. Another experiment was done on the anionic W À n clusters [16], and was found that for clusters smaller than W À 9 , molecular adsorption of nitrogen was thermodynamically more stable with respect to the dissociative chemisorption.…”

Interaction of Cu cluster anions (Cu-n, n = 8–11) with oxygen

“…One can get a better understanding of the chemisorption energetics of diatomic molecules on clusters by comparing results of the chemisorption of atomic and molecular species. Interestingly, we found that on some metal clusters, molecular chemisorption of diatomic molecules is more stable than dissociative chemisorption [21][22][23][24].…”

“…As it is shown in Figure 1, the mass-resolution is high enough to resolve different isotopes of Cu. More detailed information on our experimental set-up can be found in references [21][22][23][24]. The masses of the Cu n−1 O 6 and Cu n O 2 clusters are separated by 1 atomic unit, and therefore, discrimination between these two different clusters using our mass spectrometer is difficult for larger clusters.…”

“…To shed light to this issue, we have recently developed a new technique for the preparation of reacted metal clusters in order to compare structures of M n O − 2 (M: metal, n: number of metal atoms) prepared using molecular and atomic oxygen. This technique is a widely used one in surface science; however, this method has been utilized for the mass-selected free clusters for the first time in our group [21][22][23][24]. Using atomic oxygen, the energetic ground states of chemisorption can easily be obtained, in contrast to molecular oxygen due to its high activation barriers.…”

Chemical properties of mass-selected coinage metal cluster anions: towards obtaining molecular-level understanding of nanocatalysis

“…It should be mentioned that non-dissociative chemisorption seems to be a general phenomenon for small nanoclusters, and therefore many other catalytic reactions may proceed via nondissociatively chemisorbed species on nanoclusters. For example, N 2 chemisorbs dissociatively on W surfaces [13], but molecularly on W nanoclusters consisting of less than 15 atoms [68,69]. Stabilization of di-nitrogen and di-hydrogen species on small nanoclusters was also found on Nb and Ti cluster anions, respectively [70].…”