Isotopic Oxygen Exchange and EPR Studies of Superoxide Species on the SrF2/La2O3 Catalyst

摘要

By using the in situ IR spectroscopy,the superoxide species (O2),characterized by the O-O stretching peak at 1130 cnT1,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 (g_(xx) = 2.0001,g_(yy) = 2.0045,g_(zz) = 2.0685),showing that O2 was the only paramagnetic oxygen species detectable on the O2-pread-sorbed 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.