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用XRD、IR、XPS和SEM等方法研究了混合氧化物LiLa_(1-x)Mn_xO_2的结构和它们对甲烷氧化偶联的催化性能。结果表明,随着MnO_2的变化,可形成一系列复合氧化物,其中三元复合氧化物La_2Mn_(1-y)Li_yO_4是甲烷氧化偶联的活性相,由于Li~+部分取代Mn~(2+)形成Li~+-O~--Mn(2+)缺陷簇,增加了活性氧种的浓度和再生速度是这种氧化物具有较高甲烷偶联活性的主要原因。脉冲实验证明,CH_4脱氢生成CH_3·偶联生成C_2H_6,进一步氧化脱氢生成C_2H_4都可在催化剂表面完成,而CO和CO_2是在气相反应中生成的。在780℃C_2收率可达23.9%。
The structures of the mixed oxides LiLa 1-x Mn x O 2 and their catalytic properties for the oxidative coupling of methane were investigated by XRD, IR, XPS and SEM. The results show that a series of composite oxides can be formed with the change of MnO 2. The ternary composite oxide La_2Mn_ (1-y) Li_yO_4 is the active phase of methane oxidative coupling. Since Li ~ + partly replaces Mn ~ (2+ ) To form Li ~ + -O ~ - Mn (2+) defect clusters and increase the concentration of active oxygen species and the regeneration rate are the main reasons for the higher methane coupling activity of such oxides. Pulse experiments showed that CH_4 dehydrogenation to CH_3 coupling to C_2H_6 and further oxidative dehydrogenation to C_2H_4 can be performed on the surface of the catalyst, while CO and CO_2 are formed in the gas phase reaction. At 780 ℃ C_2 yield up to 23.9%.