Steam reforming mechanism of acetic acid for hydrogen production over the Ni/biochar catalyst: The effect of steam

Abstract

The catalytic steam reforming of biomass pyrolysis vapors on Ni-doped biochar (Ni/biochar) is an attractive approach to produce hydrogen. However, pyrolysis vapors consist of complex components, and their reforming mechanism remains comprehensively unclear. In this work, the steam reforming mechanism of pyrolysis vapors over Ni/biochar with acetic acid as the model compound was studied by density functional theory (DFT), wave function analysis, and transition state theory (TST) methods. Particularly, the role of steam in this process was primarily discussed. Acetic acid tends to interact with Ni/biochar by its dissociative OH adsorption at the active carbon position. The decomposition of acetic acid for forming carbon oxides and hydrogen is initiated by its CC and CH homolysis. The activation energy for CC homolysis increases with adding steam adjacent to reactive sites, while its addition promotes the CH homolysis (reducing from 203 kJ/mol to 151.5 kJ/mol) at the set temperatures, enhancing the competitiveness of hydrogen formation. The reactions of steam with acetic acid and its decomposed intermediates primarily result in the formation of methane, followed by carbon monoxide and methanol. These results can provide theoretical insights for the improvement and optimization of the pyrolysis and reforming technology of biomass to produce hydrogen.