Efficient in-situ removal of the trace ammonia in biomass-derived syngas by Fe-K-based biochar nano-catalysts

Trace NH₃ in biomass syngas greatly limited the widespread utilization of biomass gasification. Fe-based catalysts is a popular choice for hot gas cleanup, but with generally poor performance of NH₃ decomposition below 700 °C. In this work, biochar nano-catalysts (BN) was simply prepared by one-step catalytic pyrolysis of herb residues, in which the K promoter efficiently adjust catalytic active sites and nano-sized dispersion of Fe nano-particles (NPs) in biochar. The mechanism of NH₃ decomposition was investigated in He/H₂, and gradually extended to the simulated biomass syngas. The Fe-K-based BN catalyst (Fe-K/BN) achieved NH₃ conversion of 95.2 %, N₂ selectivity of 96.3 %, and 120-h good stability in syngas (at the condition of 550 °C with 20 vol% steam). The superior catalytic performance stems from the stable presence of FeN/Fe₃C active phases. K facilitated carbon deposition removal through steam promotion, while simultaneously inhibiting the reverse water-gas shift reaction to enhance trace NH₃ adsorption in biomass-derived syngas. This work provides a promising strategy to develop a cost-effective and stable catalyst for biomass syngas cleanup.