Oxygen molecule reaction with cluster anions

It is interesting that oxygen rich species, Cofif and 030 , exhibited O3 loss in CID experiments and underwent oxygen atom transfer as the major reaction with CO. No association of CO onto anionic cobalt oxide clusters was observed. For cationic cobalt oxide clusters, association of CO followed by loss of O3, was the major reaction channel observed, as shown for CoO " in Fig. 14.6. Association of multiple CO molecules accompanied by loss of O3 subunits was also observed for the C0O3 / and Co O cluster species indicating that these cationic centers may become quickly saturated, and therefore, poisoned at high concentrations of CO. 

Intermediates in high-temperature processes have been stabilized at low temperature after y irradiation of metal oxides and zeolites. Important early examples were oxygen anions. O, 02 and O. Some of their reactions with small molecules were also elucidated by EPR. Metal cluster ions have also been produced by radiolysis and stabilized in zeolites. Examples include alkali metal cation clusters in faujasites and silver cation clusters in zeolite A and in silicoaluminophosphate molecular sieves. Detailed information was obtained from EPR studies about their structure, thermal stability and formation of adducts. 

Hence, experimental rate constant measurements in combination with theoretical simulations show a pronounced size and structure selective activity of anionic silver clusters toward molecular oxygen due to cooperative effects. In particular, for Ag clusters with odd n, a weakly bound first O2 promotes the adsorption of a second O2 molecule which is then (for n = 3, 5) differently bound with the O2 bond elongated to 1.32 A and thus potentially activated for further oxidation reactions such as CO combustion, which have indeed been observed for larger cluster sizes [361]. 

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