Effect of Alkali Metals on CoMo2C/Al2O3 Catalysts for Syngas to Higher Alcohols

The development of catalysts for the direct one-step conversion of syngas to higher alcohols is still a challenge. In this study, different alkali metal-modified MCoMo/Al₂O₃ (M = Li, Na, K, and Cs) catalysts were prepared by impregnation and temperature-programmed carbonization process. Characterization by XRD, H₂-TPR, and XPS revealed that the introduction of alkali metals increases the crystallinity of Mo₂C, decreases the reducibility of the catalyst, as well as increases the surface high-valent Mo content. The catalysts were evaluated for activity at 300 °C, 3.0 MPa, 18,000 mL·g_Mo⁻¹·h⁻¹, H₂/CO = 2. The evaluation results found that with the increase in the electron-giving capacity of alkali metals, the CO conversion rate gradually decreased from 98.8% to 46.3%. While the alcohol selectivity showed the opposite trend, increasing from 14.4% to 54.9%. Notably, the addition of K and Cs significantly increased the alcohol selectivity in the catalyst product, from 8.3% to 50.5% and 54.9%, respectively. Moreover, the ratio of higher alcohols in the alcohol product increased significantly from 10.5% to nearly 80%. Finally, in situ DRIFT characterization of the catalysts with different alkali metal modifications was carried out to investigate the changes in the reaction process intermediates and to summarize the possible reaction routes.