Mechanistic study of bio-oil catalytic steam reforming for hydrogen production: Acetic acid decomposition

To clarify the understanding of the mechanism of bio-oil catalytic steam reforming, we selected acetic acid as a typical bio-oil model compound to study its detailed behavior in decomposition over an active stepped Ni surface by density functional theory calculations. The adsorption geometries and energies of various intermediates were reported. Linear correlations between the adsorption energy and the number of hydrogen atoms removed for CHxCOOH, CHxCOO, and CHx, species (x = 1-3) were found, with increments of 1.56, -0.81, and -1.80 eV, respectively. Thirty-seven possible elementary reactions of acetic acid decomposition were proposed, and their activation energies, reaction energies, rate constants, and equilibrium constants were calculated. Acetic acid dissociation likely started via a-carbon dehydrogenation, OH dehydrogenation, and dehydroxylation. Combined with microkinetic modeling, the most preferable decomposition pathway was suggested as CH3COOH -> CH3 CO -> CO + CH3. The rate-determining step was CH3COOH dehydroxylation to CH3CO with an activation energy of 0.68 eV and a rate constant of 3.82 x 10(8) s(-1). The formation of CH3COO was dominant at high temperatures, whereas its decomposition occurred with difficulty. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.