EPR and DFT study of the ethylene reaction with O− radicals on the surface of nanocrystalline MgO
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- 作者：Alexander M. Volodin ; Vasilii I. Avdeev…
- 关键词：O− radicals ; MgO ; DFT ; EPR ; Ethylene
- 刊名：Research on Chemical Intermediates
- 出版年：2017
- 出版时间：February 2017
- 年：2017
- 卷：43
- 期：2
- 页码：1047-1061
- 全文大小：
- 刊物类别：Chemistry and Materials Science
- 刊物主题：Catalysis; Physical Chemistry; Inorganic Chemistry;
- 出版者：Springer Netherlands
- ISSN：1568-5675
- 卷排序：43
文摘
Different radical forms of oxygen (O−, O2− and O3−) on the surface of nanocrystalline MgO are well known. It was earlier demonstrated that EPR-silent species with properties very similar to those of O− radicals exist on the surface of magnesium oxide in addition to the O− radicals observed by EPR. In this study we characterized the reactivity of these two types of O− radicals in reaction with ethylene. It was demonstrated that this reaction yields different products for observable and unobservable O− radicals. Conventional \({\text{O}}_{{3{\text{C}}}}^{ - }\) radicals generated by MgO illumination with UV light at room temperature in the presence of oxygen initiate hydrogen atom abstraction from ethylene to form secondary radicals H2C=C− with hyperfine splitting A1 = 59 G, A2 = 6 G. The \({\text{O}}_{{4{\text{C}}}}^{ - }\) radicals not observed directly by EPR were synthesized by MgO illumination in the presence of oxygen at 163 K followed by evacuation at 203 K. They were shown to react with ethylene to form an addition product with two groups of two equivalent protons with isotropic hyperfine constants A1 = 38 G and A2 = 23 G. Such radicals were obtained for the first time by reaction of O− radicals with ethylene on the MgO surface. Their concentration was approximately equal to the concentration of [\({\text{O}}_{{4{\text{C}}}}^{ - }\)·O2] complexes observed by EPR before the oxygen desorption. The structures of both radicals were simulated by DFT, and a good match between the experimental and computational results was obtained.