铈基氧化物催化剂上氧物种的EPR研究

选择ＣｅＯ２、２０％（ｍｏｌ）Ｃｅ／Ｓｒ及ＳｒＣＯ３３种甲烷氧化偶联催化剂，进行了吸附氧的ＥＰＲ及骤冷ＥＰＲ研究，对氧物种的形式、吸附方式及在反应中的作用进行了深入讨论．实验发现，氧化铈及复合催化剂很容易吸附氧分子产生Ｏ２－超氧离子，而碳酸锶表面不利于Ｏ－２的生成．Ｏ－２可以不同方式吸附于催化剂表面，不同方式吸附的Ｏ－２具有不同的氧化能力和稳定性．不同温度下骤冷可以在复合催化剂上得到几乎相同强度的Ｏ－２ＥＰＲ信号，因此Ｏ－２可能不是甲烷的选择活化中心，而是在反应条件下转化成了Ｏ２－２或Ｏ－选择性物种．复合催化剂中的ＳｒＣＯ３，对ＣｅＯ２中氧的流动性及产生氧中间体的能力起到了调节作用，抑制了过氧化．

EPR Studies of Oxygen Species over Ceria Based Oxide Catalysts

Oxygen adsorbed CeO 2, 20% (mol) Ce/Sr and SrCO 3 catalysts for oxidative coupling of methane were studied by EPR and quenching EPR techniques. The formation, adsorption and role of the adsorbed oxygen species were discussed. The results revealed that superoxide ions could be easily formed over ceria and Ce/Sr composite catalysts, while the surface of SrCO 3 was unfavorable for the formation of O - 2 ion. It is indicated that O - 2 could be adsorbed in several modes on the surface which showed different stability and oxidizing ability in reaction. O - 2 signals with almost the same intensities were obtained over Ce/Sr composite catalyst using quenching EPR, which implied that O - 2 may not be the selectively active species for the oxidative coupling of methane and might well be transformed to other selective species, like O 2- 2 etc. The oxygen mobility and adsorbing ability for dioxygen of ceria were modulated effectively by SrCO 3 in the composite catalyst, which inhibited the deep oxidation of ceria for the oxidative coupling of methane.