Density functional theory calculations and microkinetic modeling were used to study the decomposition mechanisms of the bio-oil model compound formic acid over a cobalt-stepped surface. Zero-point-energy-corrected activation barriers and reaction energies and the rate and equilibrium constants of various elementary reactions were obtained. Formic acid dissociation likely starts from dehydrogenation and dehydroxylation, with activation barriers of less than 0.5 eV. The generation of an HCOO intermediate is thermodynamically favored, but such a compound is energetically difficult to convert. COOH formation is fast and dominant at low temperatures, and it is converted rapidly after 450 K. The most favorable formic acid decomposition pathway is HCOOH -> COOH -> CO. Its rate-determining step is CO-OH scission, with an activation barrier of 0.66 eV and strong exothermicity of -1.19 eV.