Deactivation of nickel/biochar catalyst through metal-volatiles interaction in pyrolysis of poplar sawdust loaded with nickel salt.

Metal/biochar is an important category of catalyst that can be prepared via direct impregnation of metal salt to a biomass feedstock. However, during pyrolysis of metal salt@biomass for catalyst preparation, metal-volatiles interaction might affect exposure or dispersion of metal species. To verify this, loading of nickel acetate to poplar sawdust directly and to the sawdust-derived biochar was conducted to prepare Ni/biochar and biochar/Ni at 500 or 750 °C, aiming to understand the effect of metal-volatiles interaction on exposure of nickel species in resulting Ni/biochar. The results indicated Ni species catalyzed cracking, dehydrogenation, and reforming reactions in sawdust pyrolysis, producing more bio-oil/gases at the expense of biochar and also making biochar of higher aromatic degree with improved thermal stability. The in-situ IR characterizations also evidenced high activity of Ni towards dehydration and cracking of carbonyls for enhancing aromatization of biochar. In biochar/Ni catalysts prepared via loading nickel to biochar, little metal-volatiles interaction existed and nickel species weakly interacted with the biochar, resulting in remarkable migration and agglomeration of nickel, forming nickel size of 2–3 times larger than that in Ni/biochar. However, biochar/Ni possessed higher capability for adsorption/activation of H 2 , thus exhibiting superior catalytic activity than Ni/biochar for hydrogenation of phenolics. [Display omitted] • Ni accelerates removal of O-containing species in pyrolysis, enhancing aromatization of Ni/biochar. • In-situ IR characterization shows superior activity of Ni for dehydration, dehydrogenation, and cracking. • Migration of Ni in biochar/Ni prepared from impregnating biochar forms larger Ni size. • Ni in Ni/biochar is partially covered by deposits from cracking/polymerization of volatiles. • Biochar/Ni shows higher capability for H 2 adsorption and hydrogenation than Ni/biochar. [ABSTRACT FROM AUTHOR]