Coconut shell char-supported Fe-Ni bimetallic alloys catalysts for enhanced green hydrogen production via ex-situ catalytic pyrolysis of poplar wood sawdust

Coconut shell char-supported Fe-Ni bimetallic alloys catalysts synthesized via facile impregnation-reduction method. • FeNi 3 /C delivers 8.9 times higher H 2 yield than non-catalytic pyrolysis via synergistic alloy and confinement effects. • Cyclic experiments on the FeNi 3 /C catalyst show a decrease in H 2 concentration but still better than non-catalytic pyrolysis. • FeNi 3 /C exhibits broad adaptability to cellulose, hemicellulose, and lignin feedstocks for hydrogen production. Catalytic pyrolysis of lignocellulosic biomass offers a carbon-neutral pathway for sustainable green hydrogen production, yet its industrial deployment is severely hindered by excessive tar formation, low hydrogen selectivity, and rapid catalyst deactivation. Rational design of high-performance, low-cost catalysts remains the core challenge to address these bottlenecks. Herein, a series of coconut shell char-supported Fe-Ni bimetallic alloy catalysts with a fixed total metal loading of 5 wt% were synthesized via a facile impregnation-hydrogen reduction method, and systematically evaluated for ex-situ catalytic pyrolysis of poplar wood sawdust (PWS) to hydrogen. The effects of Fe/Ni molar ratio on the crystalline structure, textural properties, metal dispersion, electronic state, and catalytic performance were comprehensively investigated. The results reveal that the FeNi 3 /C catalyst exhibits the optimal catalytic activity, achieving a hydrogen content of 36.55 vol% and a hydrogen yield of 11.49 mmol/g biomass-daf , which is approximately 8.9 times higher than that of non-catalytic pyrolysis and outperforms both monometallic Fe/C and Ni/C counterparts. This superior performance originates from the strong Fe-Ni synergistic effect coupled with the micropore confinement effect of the coconut shell char support. The alloy formation not only enhances metal dispersion (average particle size of 7.89 nm) and promotes the generation of highly active metallic Fe 0 and Ni 0 sites, but also simultaneously accelerates tar cracking and water-gas shift (WGS) reactions. Cyclic stability tests demonstrate that the hydrogen yield and content gradually decrease over eight consecutive runs. Despite this decay, the spent catalyst retains a hydrogen yield (2.66 mmol/g biomass-daf ) that is still superior to that of non-catalytic pyrolysis (1.29 mmol/g biomass-daf ) and the bare carbon support (1.93 mmol/g biomass-daf ). However, the substantial performance loss highlights the need for future optimization of the support structure to enhance its resistance to micropore collapse and for the development of effective regeneration strategies. XPS analysis of the spent catalyst reveals that the metallic Ni 0 signal becomes undetectable on the surface, indicating severe surface oxidation or encapsulation, which is a primary cause of deactivation. Furthermore, the catalyst shows broad applicability to the three major lignocellulosic components, with hemicellulose identified as the primary contributor to hydrogen production. This work provides an efficient and low-cost bimetallic catalyst formulation, and offers valuable guidance for the development of biomass pyrolysis for renewable hydrogen production. Download: Download high-res image (312KB) Download: Download full-size image