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The active oxygen species and active sites for MOC(methane ox-idative coupling)over TiO_2-based catalysts are studied by ESR method.Oxy-gen chemisorption on TiO_2,La/TiO_2 and Li/TiO_2 was measured by dynamicESR technique from 295 K to 105 K.The process of oxygen adsorption onTiO_2 is discussed.The spectra show that O_2~- ions exist largely on TiO_2 but lit-tle on Li/TiO_2 due to the decrease of surface density of electrons caused bythe substitution of Li~+ for lattice Ti~(4+) in Li/TiO_2.O~- was not detected on allsamples.Both O_2~- and O~- are not likely to be the active species in MOC reac-tion.Two triplet peaks in ESR spectra of Li/TiO_2 are attributed to Ti~(3+)(Ⅱ)and Ti~(3+)(Ⅲ)of low coordination numbers,which are active in the presenceof oxygen.Sites of low coordinated Ti~(3+) or Ti~(4+) are suggested to be responsi-ble for the formation of active oxygen species.
The active oxygen species and active sites for MOC (methane ox-idative coupling) over TiO 2-based catalysts were studied by ESR method. Oxy-gen chemisorption on TiO 2, La / TiO 2 and Li / TiO 2 was measured by dynamic ESR technique from 295 K to 105 K The process of oxygen adsorption on TiO 2 is discussed. The spectra show that O_2 ~ - ions exist largely on TiO_2 but lit-tle on Li / TiO_2 due to the decrease of surface density of electrons caused by the substitution of Li ~ + for lattice Ti ~ (4+) in Li / TiO_2.O ~ - was not detected on allsamples. Bout O_2 ~ - and O ~ - are not likely to be the active species in MOC reac tion. Two triplet peaks in ESR spectra of Li / TiO_2 are attributed to Ti ~ (3 +) (Ⅱ) and Ti ~ (3 +) (Ⅲ) of low coordination numbers, which are active in the presenceof oxygen.Sites of low coordinated Ti ~ (3+) or Ti ~ (4+) are suggested to be responsi-ble for the formation of active oxygen species.