助剂对Co/Al2O3催化剂浆态床费托合成反应性能影响

考察了ZrO₂、Ru或Pt助剂对Co/Al₂O₃催化剂结构及浆态床费托合成反应性能的影响。实验结果表明,添加ZrO₂助剂可阻止或降低难还原铝酸钴的形成、促进催化剂的还原、提高Co/Al₂O₃催化剂对费托合成反应的催化活性、降低甲烷选择性并提高C₅₊烃选择性。H₂-TPR表征结果表明,少量Ru或Pt助剂均能降低Co-ZrO₂/Al₂O₃催化剂中钴物种还原温度(Co₃O₄→CoO和CoO→Co⁰),提高催化剂的还原度,催化剂呈现出良好的CO加氢反应活性。此外,催化剂组分间浸渍次序对费托合成反应性能有重要影响,载体γ-Al₂O₃先浸渍Zr组分,可有效抑制难还原化合物形成;Co、Ru组分共浸渍加强了Co和Ru组分密切接触程度,更利于钴物种的还原;Co、Pt组分依次浸渍更利于活性组分的均匀分布,催化剂具有最佳的费托合成反应性能。

Effect of promoters on the performance of Co/Al2O3 catalysts for Fischer-Tropsch synthesis in slurry reactors

The effect of ZrO₂, Ru and/or Pt promoters on the structure and performance of Co/Al₂O₃ catalysts for Fischer-Tropsch synthesis in a slurry reactor was investigated. The results indicated that ZrO₂ modification may prevent or reduce the formation of CoAl₂O₄ phase on the catalysts and improve the reduction of cobalt species, which is beneficial to the increase of the catalytic activity, the decrease of methane selectivity, as well as the improvement of C₅₊ selectivity. Small amounts of ruthenium and platinum as promoter are able to lower the reduction temperatures of cobalt species (Co₃O₄→CoO and CoO→Co⁰) and to get a high reduction extent; as a result, the catalysts promoted with noble metals exhibit much higher activity in CO hydrogenation. Moreover, the impregnation sequence of various components also has an important influence on the performance of resultant catalysts in Fischer-Tropsch synthesis. Impregnation of γ-Al₂O₃ with Zr at first, the formation of irreducible cobalt aluminate can be prevented; co-impregnation of γ-Al₂O₃ with Co and Ru can enhance the interaction between cobalt and ruthenium, which benefits to the reduction of cobalt oxides; sequential impregnation of γ-Al₂O₃ with Co and Pt is beneficial to the dispersion of cobalt species. As a result, the sequentially impregnated catalyst Co-Pt-ZrO₂/Al₂O₃ performs excellently in the Fischer-Tropsch synthesis.