Co/ZrO_2/SiO_2催化剂上费托合成反应动力学研究 Ⅰ.反应途径分析  

Detailed Kinetic Study of Fischer-Tropsch Synthesis on Co/ZrO_2/SiO_2 Catalyst Ⅰ. Analysis of Reaction Pathways

作　　者：常杰[1] 滕波涛[1] 白亮[1] 张荣乐[1] 陈建刚[1] 徐元源[1] 相宏伟[1] 李永旺[1] 孙予罕[1] 

机构地区：[1]中国科学院山西煤炭化学研究所煤转化国家重点实验室

出　　处：《催化学报》2005年第7期614-620,共7页

基　　金：国家自然科学基金重大项目(20590361);山西省自然科学基金(20021024)资助.

摘　　要：采用单位键指标二次指数势(UBIQEP)方法对模型催化剂Co(0001)晶面进行了费托(FT)合成反应的反应能学分析,发现以不含氧的CxHy,s作为中间体的表面碳化物机理在能量上较为合理,而CH2,s作为链增长单体的链增长方式是能量上最有利的FT合成反应途径.在Co/ZrO2/SiO2催化剂上的非稳态实验研究中发现,在FT合成的操作温度范围内,H2O的生成是主要的表面O的移去方式;CO解离和表面碳物种Cs加氢可能是FT合成中的重要速控步骤;链增长过程是FT合成反应中较快的基元反应步骤;甲烷的生成具有多种不同活性的表面前驱体,导致生成的甲烷严重偏离经典的ASF分布规律.结合FT合成表面反应的研究结果,初步确定了FT合成动力学研究中需要考虑的机理模型的范围是以CO解离和表面碳物种Cs加氢为速控步骤,以CH2,s插入为链增长途径的表面碳化物机理.该结果缩小了待选动力学模型的范围.Mechanistic analysis for the Fischer-Tropsch (F-T) synthesis has been conducted to resolve the tedious task in assembling a mass of model equations in its kinetic studies. Using the unity bond index-quadratic exponential potential (UBI-QEP) method, it is found that on the model cobalt-based catalyst Co(0001) surface, the surface carbide mechanism via CH_ 2,s insertion into the oxygen-free intermediates is energetically favorable. The dissociation of CO and the first hydrogenation of surface carbon have higher active barriers than the other elementary steps. The unsteady state experiments show that the formation of H_2O is the most important way to remove the surface oxygen at the F-T synthesis temperature on Co/ZrO_2/SiO_2. The formation and consequent hydrogenation of C_ s is the rate-determining step in the reaction pathway, while the C-C coupling is a relatively faster elementary reaction. There are more carbon pools for the methane formation, and the deviation of the methane product from the classical Anderson-Schulz-Flory product distribution might be due to the multiform carbon pools. Combining the results of theoretical and experimental analysis, a framework of F-T synthesis mechanistic models is obtained. This framework is similar to the surface carbide mechanism, in which the CO_s dissociation or the surface carbon hydrogenation is the rate-determining step, and the CH_ 2,s insertion produces the final hydrocarbons. But the detail forms of the oxygen-free intermediates (alkyl or alkylidene) in the carbon chain propagation cannot be discriminated. This will be resolved by the kinetic analysis in the next part of this series work.

关 键 词：钴基催化剂 费-托合成 反应动力学 反应途径 反应能学分析 非稳态实验 

分 类 号：O643.32[理学—物理化学]