Temperature dependence of the reactions of small cobalt clusters with deuterium

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Abstract
The kinetics of the reactions of cobalt clusters (Con, n=9–21) with deuterium are studied over the temperature range 133–373 K. The measured rate constants for the dissociative addition of the first D2 molecule to Con, and their temperature dependences, are found to be strongly dependent on cluster size. Co10–13 and Co15–17 are relatively reactive, with their reaction rates essentially independent of temperature, suggesting no significant reaction barrier for deuterium chemisorption. The reaction rate of Co20 is nearly constant above 213 K, but increases at lower temperature. For Co9 and Co14, the rate constants increase both at high and low temperatures. An increase at higher temperatures suggests the presence of activation barriers, while increases at low temperatures are interpreted as due to an increase in the initial trapping of D2 onto the clusters’ surfaces. For Co18, Co19, and Co21, evidence for more than one isomer at low temperature is found. The experimental results are discussed in terms of cluster geometrical structure and the detailed reaction mechanism.