N2O specificity, a-Oxygen and its Stoichiometric Reactions

A specificity of N2O oxidant compared to O2 is one of the most interesting points arising from benzene oxidation over FeZSM-5 zeolites. The specificity is clearly seen from the results presented in Table 7.6(118]. With nitrous oxide, benzene conversion is 27% at 623 K, whereas with dioxygen it is only 0.3% at 773 K. Moreover, the reaction route changes totally N2O leads to selective formation of phenol, while O2 leads only to the products of complete oxidation. 

Recently, interesting effects of NO and water on the formation and properties of a-oxygen were discovered. Even small amounts of NO facilitated desorption of O from the surface, strongly increasing the rate of catalytic decomposition of N2O to the 

Like 0 radicals on V and Mo oxides discussed above, Oa exhibits a very high reactivity. At room temperature, it readily oxidizes various organic molecules, including methane. This allows one to conduct single turnover reactions on the catalyst surface, providing in particular the synthesis of phenol according to the following scheme [119]  

This scheme includes a-oxygen loading (7.14), its interaction with benzene at room temperature (7.15) and product extraction from the catalyst surface (7.16). A nearly theoretical yield of phenol was obtained, with no other products detected. These results proved clearly the a-oxygen participation, which was confirmed additionally by isotopic experiments using [119, 133], 

Similar stoichiometric reactions can be conducted with other organic substrates. Beside mechanistic importance, such reactions are a convenient way for estimating the potential of a-oxygen oxidation. For that, various organic substrates were tested for their room temperature interaction with a-oxygen to identify the primary oxidation products extracted from the surface. Substrates included alkanes, cycloalkanes, alkenes and aromatics [121,122], Analysis of products showed that in all cases selective formation of hydroxylated compounds took place. 

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