Reactions of cobalt clusters with deuterium

Abstract

The kinetics of chemical reactions of cobalt clusters Con with deuterium are described. Absolute rate constants have been measured in the size range n = 7-68 at 293 K. The rate constants are found to be a strong function of cluster size, varying by a factor of 400. This size dependence is most prominent for n = 7 to 25:Co15 is the most reactive cluster, and Co7-9 and Co19-20 are particularly unreactive. Abrupt changes in the rate constants from one cluster size to the next are observed. For the clusters above n = 25, the rate constants show several less prominent maxima and minima superimposed on a slow, nearly monotonic increase with cluster size.nearly unit reaction probabilities for the clusters above Ni 9. For cobalt clusters, Smalley and coworkers [3] have studied the reactions with D2, N2, and CO in the size range n = 3-28. They detexmined the relative reaction rate and found that the Con-D2 reaction is dramatically sensitive to cluster size. Recently, Nakajima et al. [7] have reported the relative reactivity of positively charged cobalt clusters (Co~, n = 3-22) with H2. In this paper, we report studies of the chemical reactions of neutral cobalt clusters with deuterium. Absolute rate constants for the addition of the first I)2 molecule to Con have been measured at room temperature in the size range n = 7-68. PACS: 36.40+d, 82.20.Pm Experimental Method

Experimental and theoretical studies of ammonia generation: Reactions of H2 with neutral cobalt nitride clusters

“…Ho et al 35,36 have studied the gas phase reaction and saturated absorption on the surface of neutral cobalt clusters Co m (m = 7-68), and found a similar D 2 reactivity dependence on cluster size for the cluster sizes reported by Smalley and co-workers. Absolute rate constants and reaction probabilities were also determined, and temperature dependence of the rate constants for dissociative adsorption of the first D 2 molecule to cobalt clusters Co m (m = 9-21) was examined over the temperature range of 133-373 K. 35,36 The rate constants for clusters m = 10-13, 15-17 show no dependence on temperature, indicating that D 2 chemisorption reaction has no activation barrier. The rate constants for Co 9 and Co 14 increase at higher temperatures, which suggest the presence of activation barriers (8.8 and 7.8 kJ/mol, respectively).…”

Reactivity of Metal Clusters

“…Metal–hydrogen cluster reactivity has been extensively studied with a focus on iron, , cobalt, ,,,− vanadium, and niobium. − A typical example in Figure illustrates the reactivity of cationic Fe n + and V n + clusters with hydrogen (D 2 was used in order to avoid mass degeneracy). , It was found that the presence of positive charge had a substantial influence on the reaction rate for the majority of iron and vanadium clusters, ,, and the kinetics of D 2 chemisorption on Fe n + /V n + clusters exhibited a nonmonotonic dependence on n . It is interesting to mention that studies of hydrogen chemisorption onto cationic Fe n + ( n = 4–22) found a generally enhanced (although size-selective) reactivity compared to that for neutral Fe n .…”

Temperature dependence of the reactions of small cobalt clusters with deuterium

“…The rate constants at room temperature in a larger size range (n =7-68) have been presented earlier. 7 With the help of information about Co cluster geometry obtained from other experiments, these results can provide some insight into the details of the D2 dissociative adsorption on cobalt cluster surfaces.…”