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用电子顺磁共振(EPR)技术及原位FT-IR技术研究了O_2,CO_2,CH_4和C_2H_4在10wt％La_2O_3/MgO催化剂上的吸附和反应,用EPR谱观测到在至过1053K氧化处理后的催化剂表面存在O_2~-超氧离子,其g值为g_(xx)=1.999,g_(vv)=2.018,g_(zz)=2.061;来自于表面~(139)La同位素核(I=7/2)的超超精细裂分常数为A_(xx)=5.0×10~(-4)T,A_(vv)=7.6×10~(-4)T,研究表明,O_2~-是一种不稳定的表面氧种,在低温和脱碳酸根的表面上有利于O_2~-的存在.在473K左右的温度下O_2~-不与CH_4及C_1H_4反应,但在室温下可与CO_2作用生成一新的表面碳酸盐物种(红外吸收在1625cm_1,1335cm~(-1)),并导致其EPR信号消失.本文还对O_2~-和表面碳酸根在甲烷氧化偶联中的作用进行了讨论.
The adsorption and reaction of O_2, CO_2, CH_4 and C_2H_4 on 10wt% La_2O_3 / MgO catalyst were studied by EPR and in-situ FT-IR. The results of EPR spectroscopy showed that after oxidation treatment at 1053K (G) (xv) = 1.999, gvv = 2.018, and gzz = 2.061, respectively. The results from the surface ~ (139) La isotope nuclei (I = 7 / 2) is A xx = 5.0 × 10 -4 T and A vv = 7.6 × 10 -4 T, the results show that O 2 ~ - is a The unstable surface oxygen species is favorable for the existence of O_2 ~ - on the surface of low temperature and decarboxylation.O_2 ~ - does not react with CH_4 and C_1H_4 at about 473K, but can react with CO_2 at room temperature The new surface carbonate species (infrared absorption at 1625cm_1, 1335cm -1) led to the disappearance of EPR signal.The role of O_2 ~ - and surface carbonate in methane oxidative coupling was also discussed.