IN situ Confocal Microprobe Raman Spectroscopic Studies on Defective La-based Complex Oxides

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IN SITU Confocal Microprobe Raman SpectroscopicStudies on Defective La-based Complex Oxides

The adsorption of O₂ over defective La₂O₃-based OCM catalysts with anionic vacancies, and the reaction of surface oxygen species with CH₄ were studied by means of in situ confocal microprobe Raman spectra. The partially reduced oxygen species O₂^-, O₂^2-, O₂^δ- (O<δ<1 ) and even the lattice oxygen ion O^2-can be detected on the surface of O_2-pretreated La₂O₃-based catalysts. At lower temperatures (< 573 K) it is peroxide species O₂^2- or O^- that is more essential for the coupling of methane,while at higher temperature. the superoxide O₂^- and lattice oxygen species O^2-are rather important. It is easier for fluoride-containing La₂O₃-based catalysts to induce the oxygen species with fewer negative charges and the basicity of the cat- alyst surface is weakened, so that the C₂ selectivity for OCM reaction is improved.