We have studied the reaction mechanism of deoxygenation of propanoic acid to alkanes over Pd(111) model surfaces by a combination of microkinetic modeling and density functional theory calculations. Approximate, coverage-dependent adsorption energies of CO and H have been implemented in a microkinetic model that shows that the decarbonylation mechanism is slightly preferred over the decarboxylation mechanism at various H-2 partial pressures. The most significant decarbonylation pathway proceeds via dehydrogenation of the acid to yield CH3CHCOOH which illustrates the important role of a-carbon dehydrogenation steps, followed by dehydroxylation to yield CH3CHCO which further dehydrogenates to CHCHCO. Finally, facile C-CO bond scission occurs to yield CO and acetylene which gets hydrogenated to ethane. Overall, the dehydroxylation of CH3CHCOOH and to a lower degree the removal of the hydrocarbon pool from the surface and the dehydrogenation of the alpha-carbon of the reactant are found to be the rate-controlling steps. (C) 2013 Elsevier Inc. All rights reserved.