Isotopic Oxygen Exchange and EPR Studies of Superoxide Species on the SrF2/La2O3 Catalyst |
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Authors: | Lihua Wang Xiaodong Yi Weizheng Weng Chunxi Zhang Xin Xu Huilin Wan |
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Affiliation: | (1) State Key Laboratory of Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, P. R. China;(2) Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100080, P.R. China |
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Abstract: | By using the in situ IR spectroscopy, the superoxide species (O2−), characterized by the O–O stretching peak at 1130 cm−1, was detected on the SrF2/La2O3 catalyst at temperatures up to 973 K. The introduction of 18O2 isotope caused the 1130 cm−1 peak to shift to lower wavenumbers (1095 and 1064 cm−1), consistent with the assignment of the spectra to the superoxide species. A good correlation between the rate of the disappearance
of the O2− species and that of the formation of C2H4 was observed, suggesting that O2− was the active oxygen species responsible for the oxidative coupling of methane (OCM) on the SrF2/La2O3 catalyst. This conclusion was reinforced by the EPR experiments (gxx = 2.0001, gyy = 2.0045, gzz = 2.0685), showing that O2− was the only paramagnetic oxygen species detectable on the O2-preadsorbed SrF2/La2O3 catalyst. These results suggest that superoxide O2− can be a stable active oxygen species, whose role in the OCM reaction cannot be overlooked. |
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Keywords: | Isotopic oxygen exchange In situ IR EPR Superoxide species Methane oxidative coupling |
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