In situ IR and pulse reaction studies on the active oxygen species over SrF2/Nd2O3 catalyst for oxidative coupling of methane

Pulse reaction method and in situ IR spectroscopy were used to characterize the active oxygen species for oxidative coupling of methane (OCM) over SrF2/Nd2O3 catalyst. It was found that OCM activity of the catalyst was very low in the absence of gas phase oxygen, which indicated that lattice oxygen species contributed little to the yield of C2 hydrocarbons. IR band of superoxide species (O2−) was detected on the O2-preadsorbed SrF2/Nd2O3. The substitution of 18O2 isotope for 16O2 caused the IR band of O2− at 1128 cm−1 to shift to lower wavenumbers (1094 and 1062 cm−1), consistent with the assignment of the spectra to the O2− species. A good correlation between the rate of disappearance of surface O2− and the rate of formation of gas phase C2H4 was observed upon interaction of CH4 with O2-preadsorbed catalyst at 700 °C. The O2− species was also observed on the catalyst under working condition. These results suggest that O2− species is the active oxygen species for OCM reaction on SrF2/Nd2O3 catalyst.