Effects of Zn and Mn Promotion in Fe-Based Catalysts Used for COx Hydrogenation to Long-Chain Hydrocarbons

The promoting effect of Mn and Zn on the performance of Fe-based catalysts has been comparatively investigated in the CO x hydrogenation to heavy hydrocarbons in the presence of H 2 -deficient streams.To this scope, two catalysts have been prepared by coprecipitation, followed by impregnation with Cu and K, and tested at 220 °C and 30 bar g after an activation treatment with syngas.Both catalysts have been found to be active and selective to long-chain hydrocarbons in the presence of either H 2 /CO or H 2 /CO 2 mixtures.Despite lower catalyst reducibility, the presence of Zn has resulted in higher CO x conversion rates.Furthermore, the Zn-promoted catalyst converted CO x into heavier and less-saturated hydrocarbons.These results are consistent with a role of Zn in promoting the catalyst basicity, which is a key property to keep low the superficial H/C ratio and to slow chain termination reactions as well as secondary olefin hydrogenations.