甲烷在Sm_2O_3上氧化偶联制C_2烃的研究——Ⅰ.Na_2CO_3和过渡金属氧化物的助催化作用  

OXIDATIVE COUPLING OF METHANE OVER Sm_2O_3 CATALYST I. PROMOTION OF Na_2CO_3 AND OXIDES OF THE FIRST TRANSITION METAL SERIES

作　　者：邱凤炎[1] 沈师孔[1] 李树本[1] 

机构地区：[1]中国科学院兰州化学物理研究所

出　　处：《分子催化》1990年第2期112-121,共10页Journal of Molecular Catalysis(China)

摘　　要：本文用XRD、IR、TG、DTA和催化反应色谱法研究了添加Na_2CO_3和第一过渡系列金属氧化物对Sm_2O_3甲烷氧化偶联催化性能的影响。结果表明;随Na_2CO_3含量的逐渐变化,C_2烃的产率和选择性呈现一个复杂的变化过程,0.2wt％CoO的加入使Sm_2O_3丧失了甲烷氧化偶联的活性,而提高了深度氧化活性,CO_2成为唯一的氧化产物;然而,同样量的CoO加入7.8wt％ Na_2CO_3/Sm_2O_3中,却明显提高了生成C_2烃的产率和选择性,其它过渡金属氧化物对7.8wt％ Na_2CO_3/Sm_2O_3的影响与这些氧化物的氧交换性质存在着平行关系,而与它们的表面Me=O键能成反比。本文从Sm_2O_3的n型电导的杂质效应及不同晶相间的相互作用,对催化剂表面氧的吸附量和O^-的吸附强度的影响方面讨论了助剂的作用。Effect of added Na2CO3 and Group I transition metal oxides on the catalytic properties of Sm2O3 in oxidative coupling of methane has been studied using XRD, FTIR, DTA, DG and catalytic reaction. For oxidative coupling of methane to C2 hydrocarbons, reaction conditions were generally T=750℃, air/CH4 = 1.0/1.0 ( mol ), total gas space velocity 6000 ml· g-1 · h-1. The change of yield was found to be parallel to that of selectivity to C2 hydrocarbons over a series of Na2CO3/Sm2O3 catalysts, and quite complicated with the increase of Na2CO3 content. The addition a quite small amount of Na2CO3 (0.2 wt% ) caused a sudden decline of catalytic performance of the Sm2O3 catalyst. While a 10 wt% addition of Na2CO3 raised the yield and improved the selectivity significantly. The results obtained agree with the effect of Na+ content on n-type conductivity of Sm2O3. As the Sm3 + ions in the lattice were replaced by a small amount of Na+, which has a smaller ionic radius than Sm3 + , the n-type conductivity of the Sm2O3 will decrease. When the Na2CO3 content is increased say to 7.8 wt%, the Na + enhance will occupy the interstitial position and therefore the n-type conductivity of Sm2O3. Change of the n-type conductivity directly affects the step of O2 + 2e → 2 Os-. As the content of Na2CO3 exceeds 10 wt%, the activity of the catalyst will progressively decrease with the increasing Na2CO3 content owing to partial deactivation of an active oxygen species bonded more strongly with the surface. However, a second peak in activity appears at about 50 wt% Na2CO3. This may be ascribed to the formation of Na2CO3 crystals and the subsequent synergistic effect of the two crystalline phases of Sm2O3 and Na2CO3. This may be confirmed by comparing the results of the two catalyst samples prepared by mechanical mixing and by impregnation method described in our work. The C2 hydrocarbon yield for Na2CO3/Sm2O3 catalysts doped by oxides of metals of the first transition metal series changes with the metal in the same fashi

关 键 词：甲烷 氧化钐 氧化偶联 C2烃 

分 类 号：O622.1[理学—有机化学]