铈助剂对Co/SiO_2催化剂上费托合成反应性能的影响

Effect of CeO_2 Loading on Catalytic Performance of Co/SiO_2 for F-T Synthesis Reaction

考察了铈助剂对钴基催化剂上费托合成反应性能的影响 ,并进行了TPR和XRD等表征及瞬变应答研究 .结果表明 ,加入铈助剂后 ,催化剂的活性和C5+ 烃类的选择性有显著提高 ,且C5+ 烃类分布有明显改变 ,有利于中间馏分油的生成 .CODEX软件优化表明 ,当n(Ce) /n(Co) =0 2～ 0 3 ,w(Co) =10 % ,焙烧温度为 740K时 ,在GHSV=5 0 0h-1,p =1 2MPa,T =483K的反应条件下 ,C5+ 烃类收率可达 83 %左右 .根据实验结果 ,可以推测在钴基催化剂表面存在弱、中、强三种化学吸附的CO物种 ; CH2 基团可能通过强度适中的化学吸附CO直接加氢生成 ;强化学吸附的CO是指离解吸附的CO ,可发生歧化反应生成CO2 和积炭 ,并覆盖部分活性位 ;加入铈助剂能抑制强化学吸附的CO生成 。

A series of Co-CeO2/SiO2 catalyst samples with different CeO2 contents were prepared and characterized, and their catalytic performance for F-T synthesis reaction was measured. It was found that the addition of ceria not only enhanced the catalytic activity and the selectivity for C5+ hydrocarbons, but also favored the formation of middle distillates. The reaction temperature, calcination temperature and CeO2 loading have considerable effects on the catalytic performance of the catalyst. The optimized catalyst samples, with w(Co) = 10% and n (Ce)/n (Co) = 0.2 similar to 0.3, gave 83% similar to 86% of C5+ yield under the reaction conditions of GHSV = 500 h(-1), T = 483 K and p = 1.2 MPa. In order to explain the experimental results, it is presumed that there are three different kinds of CO species, i.e. weakly, moderately and strongly chemisorbed CO, on the cobalt-based catalysts. The strongly chemisorbed CO species easily leads to the formation of CO2 and coke deposit. The moderately chemisorbed CO species are active for F-T synthesis reaction. The CeO2 promoter can play the role to hinder the fort-nation of strongly chemisorbed CO species and favor the formation of moderately chemisorbed CO species.