一次还原气氛对还原-氧化-还原预处理Co/SiO_2催化剂费托合成反应性能的影响

Effect of First Reduction Atmosphere on Activity of Reduction-Oxidation-Reduction Activated Co/SiO_2 Catalyst for Fischer-Tropsch Synthesis

采用X射线衍射、元素分析、透射电子显微镜、Raman光谱、热重分析和H_2-程序升温还原等方法研究了一次还原气氛(H_2、CO、合成气、先H_2后CO、先CO后H_2)对还原-氧化预处理Co/SiO_2催化剂结构的影响,并考察了再经H_2二次还原后催化剂的费托合成反应性能。表征结果显示,一次还原气氛为H_2或先H_2后CO时,催化剂的活性相主要是面心立方钴,后者积碳严重;一次还原气氛为CO、先CO后H_2或合成气时,催化剂中出现面心立方钴和六方钴的混晶,前两者有积碳生成。费托合成反应结果表明,一次还原气氛分别为H_2、CO和合成气时,催化剂活性相近;一次还原气氛为先CO后H_2时,CO转化率最高(67.55%);一次还原气氛为H_2时,甲烷选择性最低(7.49%)。

Effects of different atmospheres （H2, CO, syngas, H2 and CO in succession, or CO and H2 in succession） in first reduction on crystalline structure of reduction-oxidation activated Co/SiO2 catalyst were studied by means of XRD, TEM, Raman spectrometry, TG, H2-TPR and elemental analysis. The second reduction was carried out in 1-12 only. Catalytic activity of reduction-oxidation- reduction activated Co/SiO2 catalysts for Fischer-Tropsch synthesis was investigated concerning the atmospheres of first reduction. Face centered cubic metallic cobalt species （2θ is 44.2°） were observed in both catalysts after first reduction in atmosphere of H2 and in H2 and CO in succession. Coke deposition in latter case was heavy. Cubic metallic cobalt species together with hexagonal metallic cobalt species were observed after first reduction of catalysts in atmosphere of CO, CO and H2 in succession, and syngas, respectivity. Carbon deposition was observed in fist two cases. The catalysts after first reduction in H2, CO and syngas showed similar CO conversions in Fischer-Tropsch synthesis. The catalysts after first reduction in atmosphere of CO and H2 in succession showed the highest CO conversion（67.55% ） and catalyst after first reduction in H2 showed the lowest CH4 selectivity（7.49% ）.