CO₂ hydrogenation to liquid hydrocarbons via modified Fischer–Tropsch over alumina-supported cobalt catalysts: Effect of operating temperature, pressure and potassium loading

The effect of promoting 15%Co/Al₂O₃ catalyst with potassium on CO₂ hydrogenation to longer-chain hydrocarbons was investigated. The catalysts used in this study were synthesized using an incipient wetness impregnation of the support with nitrate solutions. All catalysts were supported on γ-alumina and promoted with potassium (0 – 8%). The synthesized catalysts were characterized by XRD, BET, XPS, TPR and CO₂-TPD analyses. The catalysts were evaluated for CO₂ hydrogenation using a fixed-bed tube reactor. The CO₂ conversion was found to increase with both the reaction temperature and pressure. The TPR data revealed that potassium limited the reduction of the catalyst, decreased the selectivity to methane and increased the selectivity to C₂₊ hydrocarbons. The maximum C₂₊ yield of 10.2%, with CO₂ conversion of 42.3%, was obtained when 6 wt.% of potassium was added to the catalyst. It is believed that during the CO₂ hydrogenation process over the catalysts that were promoted with potassium, CO₂ is first converted to CO via reverse–water–gas–shift reaction, followed by subsequent hydrogenation of CO to hydrocarbons.