FeMn、FeMnNa和FeMnK催化剂上合成气制低碳烯烃的比较

研究了钠、钾助剂对FeMn 合成低碳烯烃催化剂结构及性能的影响. 低温N₂吸附、X射线光电子能谱（XPS）、X射线衍射（XRD）、H₂程序升温还原（H₂-TPR）、CO/CO₂程序升温脱附（CO/CO₂-TPD）、Mössbauer 谱和CO+H₂反应的研究结果表明，增加Mn助剂含量促进了活性相的分散和低碳烯烃的生成，而过多锰助剂在催化剂表面的富集则降低了费托合成反应的CO转化率；钾助剂和钠助剂的加入均抑制了催化剂的还原并且促进了CO₂和CO的吸附. 比较还原后（H₂/CO摩尔比为20）和反应后（H₂/CO摩尔比为3.5）催化剂的体相结构可以发现，在FeMn、FeMnNa和FeMnK催化剂中，由于钾助剂的碱性和CO吸附能力较强，因此体相中FeC_x的含量相对较高；而活性测试结果表明，FeMnNa催化剂拥有最好的CO转化率（96.2%）和低碳烯烃选择性（30.5%，摩尔分数）.

Comparison of FeMn,FeMnNa and FeMnK Catalysts for the Preparation of Light Olefins from Syngas

The influence of sodium and potassium promoters on the structure and reaction behavior of an FeMn catalyst toward light olefin synthesis from syngas was investigated by N₂ adsorption, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), H₂ temperature-programmed reduction (H₂-TPR), CO/CO₂ temperature-programmed desorption (CO/CO₂-TPD), Mössbauer spectroscopy (MES) and CO+H₂ reaction. We found that an increase in manganese improves the dispersion of the active Fe component and light olefin selectivity; however, excessive enrichment with the Mn promoter on the catalyst surface suppresses CO conversion. Potassium and sodium inhibit the reduction of the catalyst in H₂ and improve the adsorption of CO₂ and CO because of the enhanced surface basicity of the catalysts. After reduction with syngas (n_H2/n_CO=20) and reaction with syngas (n_H2/n_CO=3.5), the analysis of the bulk structure was compared with those of the FeMn, FeMnNa, and FeMnK catalysts. The results show that FeC_x is found in relatively high levels in the FeMnK catalysts because of the stronger alkalinity and adsorbability of CO. However, Fischer-Tropsch synthesis (FTS) results indicate that sodium and potassium improved the selectivity toward light olefins. The best catalytic performance was achieved by the FeMnNa catalyst. Its CO conversion and light olefins selectivity were 96.2% and 30.5% (molar fraction), respectively.