Construction Of Biochar-Supported Fe-Based Nanometal Catalyst And The Catalytic Cracking Behaviour Of Biomass Tar

Biomass gasification is considered as a critical way to achieve efficient and low-carbon utilization of biomass resources.While the presence of tar is a bottleneck for biomass gasification technology.The tar not only reduced the gasification efficiency,but also caused the blockage,pollution,and erosion of equipment.Among various tar removal technologies,the catalytic cracking method is widely regarded as the most effective and promising method for tar removal during biomass gasification process.Developing an efficient and inexpensive catalyst to remove tar is critical to biomass gasification technology.However,the existing catalysts suffer from low activity and easy carbon accumulation and difficult regeneration after deactivation.Based on this background,this paper presented an experimental study on the preparation of iron-based biomass char catalysts.The main contents and related conclusions are as follows:Firstly,Fe embedded graphene nanoshell/carbon nanofibers catalysts were prepared from sawdust and FeCl₃·6H₂O by adjusting the carbon thermal reduction temperature and atmosphere.The characterization results showed that CO₂ etching improved the porosity of the catalysts and increased the content of Fe₀ under the carbothermal reduction temperature of 800℃.During CO₂ etching and catalysis of FeCl₃,the prepared catalyst formed a structure in which a large number of carbon nanofibers/graphene shells wrapped metallic iron deposited on the porous carbon support.Compared with other catalysts,the Fe@C800C1 catalyst showed good catalytic performance at 700℃ with a high tar conversion of 90.4%.After four cycles,the tar removal efficiency remained at 90.0%.Secondly,Fe-Mo@char catalysts were prepared using the same carbothermal reduction method.The characterization results of fresh catalysts showed that the addition of the Mo species enhanced the carbon solubilization process on the surface of the metal Fe nanoparticles during carbothermal reduction process.Thus the Mo species not only promoted the formation of Fe₃C-Mo₂C active centres,but also enhanced the etching effect of the metal nanoparticles on the carbon support,which enriched the mesoporous structure of the catalysts.The tar conversion efficiency of Fe-Mo_0.5@char catalyst reached 91.05% at the catalytic cracking temperature of 700℃.The Fe₃C-Mo₂C active sites promoted the cracking of multi-ring tar compounds and removed unstable oxygen-containing functional groups from the benzene ring,facilitating the formation of phenolics with stable structures.Finally,a red mud/biochar catalyst was prepared by in-situ carbothermal reduction of sawdust and red mud.Through the carbothermal reduction of process,the catalyst was not only endowed with a porous carbon structure,but also reduced Fe₂O₃ in red mud to Fe₀,which was beneficial to improving the catalytic activity and stability of the catalyst.The tar conversion efficiency of RM/SD catalyst reached 88.70% at the catalytic cracking temperature of 700℃.The catalytic activity and deactivation progress of RM/SD catalyst were investigated by a variety of characterizations for the chemical states,crystallite sizes and pore structure of RM/SD catalyst after different cycles.During the catalytic process,alkaline and alkaline earth metals in red mud migrated to the surface of catalyst and cooperated with Fe active phase,which promoted the gasification of coke and alleviated the rapid deactivation of catalyst derived from coke deposition.Meanwhile,the presence of carbon support delayed the oxidation of metal active phase and made the catalyst keep a good tar catalytic cracking performance.In summary,the preparation process of biochar-supported iron-based nanometallic catalysts was optimized to achieve efficient and stable cracking of tar in this study.The results will contribute to breakthroughs in the removal of biomass tar during biomass gasification process.