Synthesis of modified char-supported Ni–Fe catalyst with hierarchical structure for catalytic cracking of biomass tar

The ubiquitous challenge of tar problem has limited the further development of biomass pyrolysis/gasification. In view of this, the directional construction of modified char-supported Ni–Fe catalyst by hydrothermal carbonization followed by heat treatment to strengthen tar cracking was reported in this study. At the optimized temperature of 700 °C for catalytic cracking, the corresponding tar conversion efficiency of catalyst appeared to be 95.46% with the superior catalytic performance of tar. With the presence of such catalyst, the relative content of polycyclic aromatic hydrocarbon (PAH) compounds in residue tar was drastically reduced due to the high activity of Ni–Fe alloy active phases for the cleavage of tar macromolecules. The hierarchical pore structure derived from the dense carbon nanofiber shell layer and porous carbon core reduced the resistance of tar macromolecules diffusion and promoted the contact with metallic active sites. The Fe atoms enriched on the surface of Ni–Fe alloy with a high oxygen affinity promoted the catalytic cracking reaction of tar. The coated metallic active sites with multi-layer graphitic carbon prevented the catalyst from deactivation and sintering. The results are expected to establish the theory foundation and construction method of char-supported Ni–Fe catalyst for tar catalytic cracking in the industry.