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Reaction rates and saturation values were determined for H2 dissociative chemisorption on positive niobium cluster ions in an FT-ICR apparatus. Clusters with 8,10,12, and 16 atoms were found to be particularly unreactive, in remarkable agreement with the reactivity patterns observed previously for neutral niobium clusters. Saturation coverage for most clusters was found to occur near a hydrogen/niobium ratio of 1.3, although some clusters (8–12,16, and 19) reached effectively inert compositions at considerably lower coverages. Several examples were found of clusters having two isomeric forms with different reactivities. One form of Nb+19 was found to readily react with H2, whereas a second form representing one-third of the original sample of 19 atom clusters was completely inert to H2 chemisorption under the same FT-ICR conditions. The geometrical shape of these niobium clusters must therefore have a critical effect on reactivity.
Elkind et al. (Fri,) studied this question.