Preparation Of Iron Carbide Nanocatalyst Derived From Biomass For Fischer-tropsch Synthesis

With the rapid development of Chinese economy and the increasing demand for petroleum resources,it is particularly urgent to develop new and renewable energy resources and find alternative ways to replace petroleum resources effectively.Fischer-Tropsch synthesis(FTS)has attracted people's attention as a well-known and long-established commercial technical route to produce a wide range of synthetic paraffins and olefins from syngas comprising primarily H₂ and CO,derived from non-petroleum carbon sources,such as coal,biomass and natural gas.Especially,for coal-and biomass-based syngas with low H₂/CO ratio,iron-based catalysts are preferentially applied in FTS industrial implementation,depending largely on abundant reserves,low price,adequate catalytic performance for water-gas shift reaction and impressive selectivity for olefins production.In addition,iron carbides have been proved to be the main active phase of iron-based FTS catalysts,but the current preparation methods still have some limitations such as complex preparation methods,high cost,etc.As the only renewable organic carbon source,low-cost and readily available biomass has long been established and developed to mass-produce functionalized carbon materials.Herein,an extremely facile and green strategy was executed for the first time to in-situ construct K-Fe₃C@C nanohybrids directly by one-pot carbonization of the pomelo peel impregnated with Fe(NO₃)₃.The pyrolytically self-assembled nanohybrids were successfully applied in Fischer-Tropsch synthesis(FTS)and demonstrated high catalytic performance.Accordingly,the optimized K-Fe₃C@C catalysts revealed excellent FTS activity(92.6%CO conversion)with highlighted C₅₊hydrocarbon selectivity of 61.3%and light olefin(C⁼_2-4)selectivity of 26.0%(light olefin/paraffin(O/P)ratio of 6.2).Characterization results further revealed that the high-performance was correlated with the in-situ formation of the core-shell nanostructure consisted of Fe₃C nanoparticles enwrapped by graphitized carbon shells,and the intrinsic potassium promoter originated in pomelo peel during high-temperature carbonization.Moreover,over ten types of biomasses chosen were comparatively studied to determine the effect of the complex organic components,inorganic minerals and sulfur content on the catalytic performance.This work provided a facile approach for the low-cost mass-fabrication of high-performance carbon-based catalysts by directly utilizing waste biomass without any chemical pretreatment or purification.In addition,utilizing citric acid derived from biomass as carbon source and reducd iron powder as iron source for the first time,Fe@C nanoparticles were prepared by a facile and green modified sol-gel method.After optimizing the condition of carbonization temperatures and the contents of iron loading,the optimized Fe@C-1/1.5 catalyst prepared from reduced iron powder showed high C₅₊selectivity(56.3%)at 97.7%high CO conversion.Moreover,the effects of different iron precursors on the FTS activity of catalysts were further investigated.It was confirmed that iron precursors could significantly affect the phase structure and catalytic performance of catalysts,and sulfur in ferrous sulfate had an obvious toxic effect on the activity of iron metals.In this paper,decreasing the use of high cost and environmental unfriendly iron salt,direct utilization of low cost reduced iron powder provided a facile method for the low-cost iron-based catalyst synthesis.