Fischer-Tropsch synthesis: Effect of CO₂ containing syngas over Pt promoted Co/γ-Al₂O₃ and K-promoted Fe catalysts

The effect of CO₂ was studied for cobalt and iron Fischer-Tropsch (FT) synthesis. CO₂ behaves differently in the presence of CO over cobalt and iron catalysts in terms of hydrogenation. A systematic increase of the CO₂ mole fraction of carbon in the feed gas mixture alters the product distribution dramatically for cobalt FT synthesis with CO₂ behaving like an inert gas at higher partial pressure of CO. With cobalt, CO appears to compete with CO₂ for adsorption. Using an iron FT catalyst, hydrogenation of CO₂ was effected due to the presence of the reverse water-gas shift activity of the catalyst which converts CO₂ to hydrocarbons through the formation of CO. Unlike the cobalt catalyst, the product distribution was only slightly altered with increasing CO₂ content in the feed gas mixture to the iron catalyst. This difference in behavior of CO₂ over cobalt and iron could be attributed to the absence of reverse water-gas shift activity on cobalt and hydrogenation of CO₂ to hydrocarbons-other than methane-will be derived through the formation of CO.