Enhanced hydrogen production and carbon suppression via a two-stage catalytic system of biochar pre-catalysis and Ni-based catalysts during biomass pyrolysis

Abstract A new two-stage catalytic system was developed to overcome the problems of low yield of hydrogen-rich gas and serious carbon deposition on the catalyst during biomass pyrolysis catalysis. The operating temperature, catalyst type and catalyst addition ratio were compared, and the optimum hydrogen production conditions were obtained (with yield reaching 52.21 wt% and the hydrogen yield reaching 29.15 vol%). The catalysts were modified by metals, including Ni, Ni–Co, Ni–Fe, Ni–Mo and Ni–Ce. Ni–Ce/Al 2 O 3 exhibited the highest tar-cracking efficiency during one-stage catalysis, attributed to the redox cycle between Ce 3+ /Ce 4+ . In order to further improve the catalytic performance, the biochar pre-catalytic layer with rich porous structure and surface functional groups was introduced. Macromolecular volatiles were selectively adsorbed by the pre-catalyst and promoted in chain reactions. Macromolecular volatiles were selectively adsorbed by the pre-catalyst, in which the tar reforming reaction was promoted, resulting in an increase in hydrogen production to 29.76–48.87 vol% in two-stage catalysis. In addition, Biochar pre-catalyst promoted free radical recombination by enhancing the formation of H 2 and H· and reducing the binding of polycyclic aromatic hydrocarbons, which effectively inhibited carbon deposition. This study provides theoretical insights and proposes a novel stepwise catalytic strategy for efficient hydrogen production from biomass, highlighting its potential for practical energy conversion applications. Highlights • Novel two-stage catalyst (biochar + Ni/Al 2 O 3 ) promoted H 2 yield (48.87 vol%) and redused carbon deposition. • Biochar pre-catalysis activated volatiles via surface functional groups, promoting tar cracking and H 2 formation. • Ni-Ce/Al 2 O 3 showed excellent performance in tar cracking through Ce 3+ /Ce 4+ redox, boosting the gas and H 2 production. Graphical Abstract