Effect of sulfur and carbon in the pyrolysis volatiles on the activity of Fe-Ni/biochar

In a fixed-bed reactor, the Fe/biochar, Ni/biochar, and Fe-Ni/biochar bimetallic catalysts for the catalytic reformation of anise pyrolysis volatiles were examined. The findings demonstrate that the Fe/biochar catalyst has high catalytic activity. When anise was used as the pyrolysis feedstock, neither the Ni/biochar catalyst nor the Fe-Ni/biochar bimetallic catalyst demonstrated catalytic activity. The effects of catalyst sintering, carbon deposition, oxidation, and poisoning were investigated. The combined effect of poisoning and carbon accumulation was found to cause severe deactivation of FeNi bimetallic catalysts. The higher the sulfur content in the biomass feedstock, the more sulfur-containing gas there will be in the volatile components from the biomass pyrolysis. The H2S and COS in these gases undergo chemisorption and chemical interaction with the active metal of the catalyst, resulting in the formation of NiS from the active component Ni in the Fe-Ni/biochar catalyst. The breakdown of organic sulfur in biomass is the primary cause of catalyst poisoning at pyrolysis temperatures of 700 °C. Microwave-assisted citric acid can reduce the organic sulfur in star anise from 0.65% to 0.17%, effectively alleviating the poisoning of Fe-Ni/biochar.