Fischer-Tropsch synthesis represents an industrially important catalytic reaction for the formation of higher hydrocarbons, starting from synthesis gas (CO and H2). A periodic, self-consistent, Density Functional Theory analysis of the elementary steps up to C2 hydrogenation on pure Fe(110), subsurface-carbon modified Fe(110), and Pt-modified Fe(110) surfaces will be presented and contrasted to the corresponding elementary steps on Cobalt surfaces.