▎ 摘　　要

Carbon-based metal catalyst has attracted wide attention in the utilization for tar catalytic cracking because of its high hierarchical porous structure and high dispersion of metal particles. In this study, sawdust was used as raw material to prepare Fe embedded graphene nanoshell/carbon nanofibers catalyst for catalytic cracking of biomass tar by impregnation followed by carbothermal reduction in CO2 atmosphere. The properties of the catalysts were evaluated by a variety of characterization methods and based on which the evolutionary mechanism was proposed. CO2 etching improved the porosity (Vtotal = 0.4187 cm3/g and BET surface area = 225.93 m2/g) and increased the content of Fe0. During CO2 etching and catalysis of FeCl3, the prepared catalyst formed a structure in which a large amount of carbon nanofibers/graphene shells wrapped metallic iron deposited on the porous carbon support. The stacking of carbon nanofibers enhanced the adsorption capacity of the catalyst to tar macromolecules. The coating of the graphene shell to the metal nanoparticles prevented the agglomeration and sintering of metal active sites, which increased the stability of the catalyst. The results indicated that the Fe@C800C1 catalyst showed good catalytic performance at 700 degrees C, and the tar conversion efficiency reached up to 90.4%. After 4 cycles, the tar removal efficiency still maintained at 90.0%.