Abstract:

Lower olefins synthesis from direct CO₂ hydrogenation over Fe-based catalysts is an important process of CO₂ utilization. Iron catalysts with different K loading (1%, 3%, 5%, 7% and 9%) prepared by thermal decomposition were used in CO₂ hydrogenation. Fe95-K5 (95%Fe-5%K,mass fraction) catalyst showed the highest activity and C₂-C₄ olefin selectivity. Further enhancement on Fe95-K5 catalytic performance was achieved by pre-treatment under three different activation atmospheres (10%H₂/Ar, 10%CO/Ar, 5%CO/5%H₂/Ar) prior to CO₂ hydrogenation. 10%CO/Ar-activated catalyst showed the highest C₂-C₄ olefin selectivity (38.1%) and chain growth probability (α=0.644). In addition, the structure evolution of Fe95-K5 during activation and CO₂ hydrogenation was characterized by X-rays diffraction (XRD), Raman and temperature-programmed hydrogenation (TPH) techniques. CO introduction in pretreat process accelerated formation of iron carbides. γ₁-iron carbide was formed after pretreating in 10%CO/Ar and 5%CO/5%H₂/Ar, while γ₂-iron carbide was produced in the hydrogenation reaction after pretreating in 10%H₂/Ar. Both carbides could promote CO₂ dissociation on catalyst surface.

Key words: CO₂ hydrogenation, Fe-K, activation atmospheres, lower olefins, structure-performance relationship

摘要：

CO₂加氢直接制取低碳烯烃是实现其资源化利用的重要途径。通过热分解法制备了5种不同K含量（1%、3%、5%、7%、9%）的Fe-K催化剂用于CO₂加氢反应，结果表明Fe95-K5（95% Fe-5% K，质量分数）催化剂具有最优的活性及C₂～C₄烯烃选择性；随后对Fe95-K5催化剂进行了10% H₂/Ar、10% CO/Ar及5% CO/5% H₂/Ar 3种不同气氛活化处理以及CO₂加氢反应。结果发现，10% CO/Ar活化的催化剂具有最高的C₂～C₄烯烃选择性（38.1%）及链增长能力（α=0.644）。此外，还通过X射线衍射、Raman、程序升温等表征技术揭示了催化剂在不同活化气氛下的结构演变历程。研究发现，10% CO/Ar与5% CO/5% H₂/Ar活化的催化剂会生成γ₁型碳化铁结构，而10% H₂/Ar活化的催化剂则会在反应过程中生成γ₂型碳化铁结构，两种碳化铁结构对CO₂解离均有促进作用。

关键词: CO₂加氢, Fe-K催化剂, 活化气氛, 低碳烯烃, 构-效关系