Role of the Ti(IV)-Superoxide Species in the Selective Oxidation of Alkanes with Hydrogen Peroxide in the Gas Phase on Titanium Silicalite-1: An In Situ EPR Investigation
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The interaction of TS-1 with gaseous hydrogen peroxide at temperatures above 373 K has been investigated by in situ EPR measurements. Treatment of TS-1 with hydrogen peroxide in the gas phase leads to a strong EPR signal, assigned to the Ti(IV)-superoxide species. In contrast to investigations with liquid hydrogen peroxide, here only one Ti(IV)-superoxide species could be detected in the EPR spectrum. The time constant of the reaction of the Ti(IV)-superoxide species detected by in situ EPR measurements was much larger than that observed for the rate of consumption of propane or propene via gas chromatographic analysis. Thus, we conclude that the superoxide species may take part in the oxidation reaction (via side reactions or the formation of unselective products), but is probably not the main responsible species in the oxidation of propane or propene.
KeywordsTitanium silicalite-1 EPR Oxidation Hydrogen peroxide Superoxide Alkanes
The authors are grateful to Prof. Rudolf Holze, Chemnitz University of Technology, for providing access to his EPR Spectrometer and to Prof. Angelika Brückner for fruitful discussions.