A Monodisperse ε′-(Co<sub><i>x</i></sub>Fe<sub>1–<i>x</i></sub>)<sub>2.2</sub>C Bimetallic Carbide Catalyst for Direct Conversion of Syngas to Higher Alcohols
Zhuang Zeng, Zhuoshi Li, Kang Li, Xiaoxue Han, Zouxuan Qi, Shaoxia Guo, Junhu Wang, Alexandre I. Rykov, Jing Lv, Yue Wang, Xinbin Ma
Abstract
Higher alcohol synthesis (HAS) from syngas through nonpetroleum carbon resources is quite prospective but still challenging owing to the unsatisfactory selectivity and catalytic stability. Here, we proposed a monodisperse ε′-(CoxFe1–x)2.2C alloy carbide catalyst derived from CoxFe3–xO4 spinel oxide nanoparticles, which was applied in the HAS reaction. The Co/Fe molar ratio showed a significant impact on the evolution of active sites, and the catalyst with a Co/Fe molar ratio of 1/2 contained the highest ε′-(CoxFe1–x)2.2C content of 80.2%, which achieved the best selectivity and space time yield toward higher alcohols (HA) as high as 38.5% and 1.932 g g(Fe + Co)–1 h–1, outperforming most of the reported modified Fischer–Tropsch synthesis catalysts for HAS. Density functional theory calculations further confirmed that the formation of ε′-(CoxFe1–x)2.2C alloy carbide became more difficult when the Co/Fe ratio exceeds 1/2. It is demonstrated that the ε′-(CoxFe1–x)2.2C exhibited moderate bonding with CO, which is crucial for the balance between CO dissociation and CO insertion, thus increasing the HA selectivity. The Co1Fe2 catalyst with a robust CoFe alloy carbide structure exhibited stable catalytic performance for over 300 h because of the inhibition of phase separation and surface carbon deposition. These insights into the formation and properties of CoFe alloy carbide may provide possibilities for the development of bimetallic catalysts for HAS.