CO2 hydrogenation was investigated with a doubly promoted (Cu, K) silica containing iron catalyst. Hagg carbide (chi-Fe5C2) is the dominant phase obtained under CO activation conditions at 543 K and 0.1 MPa and it was stable under FTS conditions typical for coal or biomass derived syngas using a H-2/CO ratio of 1:1 for at least similar to 100 h TOS. An Fe-phase change occurs (chi-Fe5C2 -> Fe3O4) after switching from H-2:CO:N-2 (1:1:2) to H-2:CO2 (3:1). The distribution of hydrocarbon products changes significantly after switching to H-2:CO2 (3:1), but then it slowly transformed to normal FTS products, albeit with over 3 times higher methane selectivity compared to FTS using H-2:CO:N-2 (1:1:2). A correlation was obtained between the rate of FTS and the % of Fe carbide indicating that iron carbide is the active phase for CO2-based FT synthesis. Irrespective of conditions (i.e., either H-2:CO:N-2 = 1:1:2 or H-2:CO2 = 3:1) and the Fe phase, the methane selectivity appears to primarily depend on the H-2/CO ratio. (C) 2012 Elsevier B. V. All rights reserved.