A mechanistic study on the decomposition of a model bio-oil compound for hydrogen production over a stepped Ni surface: Formic acid

To obtain a clearer understanding of the catalytic bio-oil reforming mechanism, we performed density functional theory calculations on the decomposition of formic acid over a stepped Ni surface. Formic acid was selected as a model bio-oil compound. Fourteen elementary reactions were considered. All the zero-point-energy corrected activation energies and reaction energies were obtained. The kinetic parameters of the reaction rate constants and thermodynamic equilibrium constants in the temperature range of 300-1000 K were revealed. COOH formation and its subsequent dissociation are energetically easier than that of HCOO. When combined with kinetic modeling, the most preferable pathway for formic acid dissociation on the surface is HCOOH -> COOH -> CO. The rate-determining step is COOH dehydroxylation to CO, associating with an activation energy of 0.51 eV and a rate constant of 5.16 x 10(9) s(-1) at 773 K. In addition, HCOO will be slowly accumulated on the surface as the temperature rises. (C) 2018 Elsevier B.V. All rights reserved.