Dependence of metal cluster reaction kinetics on charge state. I. Reaction of neutral (Nbx) and ionic (Nb+x, Nb−x) niobium clusters with D2

Abstract

The effect of charge state on niobium cluster chemisorption kinetics is explored via measurement of the relative rates of D2 activation by Nb−x, Nbx, and Nb+x containing up to 28 atoms. The presence of the + or − charge is found to have only a minor effect on rate for the majority of the clusters, with the reactivity of the ions being generally within a factor of 2.5 of the corresponding neutrals. The excess charge does, however, have a profund influence on reaction rate for a number of clusters in the 7≤x≤16 size range, which may be indicative of the importance of cluster electronic structure in the chemisorption process. Kinetic data for Nb9, Nb12, and Nb+12 are found to deviate significantly from the expected pseudo-first-order behavior, suggesting the existence of structural isomers for these species. The anomalous behavior for Nb9 and Nb12 was not observed in previous neutral Nbx chemisorption studies. The maximum uptake of D2 by niobium clusters is found to be essentially independent of charge state, but varies strongly with x, consistent with the presence of a high barrier to D–D bond activation for certain of the clusters.

Experimental vibrational spectra of gas-phase tantalum cluster cations

“…For both V + 12 and Nb +/0 12 , experiment and theory have found evidence for the presence of different isomers. 17,47,48 However, in case of Ta + 12 it is impossible to either proof or disproof the existence of isomeric structures in the molecular beam, as the vibrational spectrum shows only few and very weak peaks.…”

Theoretical study of molecular nitrogen adsorption on Wn clusters

“…As one of the key factors to understand the catalytic mechanism, adsorption behaviors of gas molecules on metal clusters have been studied widely both experimentally and theoretically [2][3][4][5][6][7][8][9][10][11]. It has been found that the adsorption properties change significantly as a function of cluster size for many systems, such as H 2 , D 2 , and N 2 on Fe n [2,3] and Nb n clusters [4][5][6][7][8], CO on different metal clusters [9], and O 2 on Au clusters [10,11]. In many cases, the different chemisorption reactivities have correlations to the electronic structures of metal clusters, such as electron affinity (EA) or ionization potentials (IP).…”

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

“…The rates of the chemisorption of H 2 , D 2 , and N 2 on Fe n , and Nb n (n = number of atoms) clusters and those of CO on different metal clusters can vary by several orders of magnitudes as a function of n [1][2][3][4][5][6]. For W n , a sharp jump of the reactivity towards N 2 chemisorption is detected at liquid nitrogen temperature as well as room temperature as n exceeds 15 [7,8].…”