还原-氧化-还原过程对Co-ZrO_2共沉淀催化剂结构及其费托合成反应性能的影响

采用程序升温还原、氮吸附、X射线衍射、Raman、XPS和H2-TPD等方法研究了还原(400℃,氢还原)-氧化(室温,暴露空气中氧化)-还原(250℃或400℃,氢还原)预处理过程对Co-ZrO2共沉淀催化剂结构的影响,考察了催化剂在不同反应器中的费托反应性能。结果表明,催化剂还原氧化前后钴物种均以Co3O4形式存在,颗粒直径无明显变化;还原氧化处理后催化剂表面钴物种含量有所下降,但H2-TPD结果显示催化剂经还原-氧化-还原后氢吸附量增加。另外,还原氧化过程能够降低催化剂表层钴物种的还原温度。反应结果表明,催化剂经还原氧化还原处理后活性明显增加,甲烷选择性降低。

Influence of reduction-oxidation-reduction treatment on the structure and catalytic performance of Co-ZrO2 for Fischer-Tropsch synthesis

Co-ZrO₂ precipitated catalyst is treated by reduction in H₂ at 400℃, Oxidation of the reduced catalyst in air at room temperature, and reduction again in H₂ at 250℃ or 400℃. The influence of this reduction-oxidation-reduction treatment on the properties of Co-ZrO₂ precipitated catalyst was investigated by TPR, N₂ physical sorption, H₂-TPD, XPS, XRD, and Raman spectra; the performance of treated catalysts in Fischer-Tropsch (F-T) synthesis was considered in both slurry phase and fixed bed reactors. The results showed that cobalt in the catalyst is in the form of Co₃O₄ with little change in particle sizes after the reduction-oxidation process. The concentration of cobalt on the catalyst surface is reduced a little after the treatment, but the amount of H₂ uptake is increased significantly. The reduction-oxidation treatment can lower the reduction temperature of surface cobalt species. As a result, the catalytic activity of Co-ZrO₂ for F-T-synthesis is improved and the selectivity to CH₄ is depressed by the reduction-oxidation treatment. Furthermore, the catalyst reduced at a relatively high temperature exhibits much better performance in the fixed bed reactor.