The Research Of Preparing Iron Carbide By Thermal Reduction For Fischer-Tropsch Synthesis

FTS has been considered to be a practical approach for producing liquid fuels and chemicals from fossil resources such as natural gas,coal as well as biomass-derived biogas.Therefore,exploring effective methods to control the nucleation and growth of supported metallic particles and eventually to design size-variable and phase-stabilized iron carbide catalysts is crucial for development of high-performance FTS catalysts.Herein,we demonstrate a coordination-assisted self-assembly route for the synthesis of high-quality ordered mesoporous carbons incorporated with highly dispersed uniform Fe nanoparticles for application in FTS to investigate the catalytic performance,which has adjustable phase state and controllable particle size.In the first part,we combined coordination-assisted self-assembly with carbothermal reduction route to synthesize ordered mesoporous carbon with uniform Fe-containing nanoparticles.The phase structures,compositions,and particle sizes of the catalysts are characterized systematically by TG,XRD,BET and TEM.The obtained catalysts have a 2-D hexagonally arranged pore structure,uniform pore size??5.6 nm?,high surface area??317 m²/g?,moderate pore volume??0.33 cm³/g?,uniform and highly dispersed?-Fe₂C,?-Fe₅C₂,?-Fe₃C nanoparticles,which depending on activation atmosphere and temperature.Constant Fe contents around 20wt%?-Fe₂C and?-Fe₅C₂ have been demonstrated to be actived in low and high temperatures FTS respectively,however,?-Fe₃C has been considered inactive.Without Na-modulated,Fe-C-400 were studied as catalysts in FTS under conditions(H₂/CO=1,10 bar,300°C,GSHV=15000 ml h^-1 g^-1_cat).The materials showed very high CO conversion levels?72.71%?,olefins selectivity?45.83%?,iron time yield(FTY=158.29?mol_COO g_Fe^-11 s^-1).The existence of Na would suppress the hydrogenation of olefins by weakening the adsorption of olefins and further enhancing the chance of carbon chain growth to increase the ratio of olefin/alkane to 9.62 and C₅₊selectivity?83.91%?.In the second part,we demonstrate a chelate-assisted coassembly route for the synthesis of high-quality ordered mesoporous carbons incorporated with highly dispersed uniform FeO_x nanoparticles.The synthesis is based on a multi-constituent coassembly process which is accomplished by slow evaporation of an water solution containing soluble resol as a carbon source,iron nitrate as a metallic precursor,citric acid as a chelating agent,and Pluronic F127 as a template.All of the Fe-C-y samples have a similar support structures and Fe content.By the utilization of the capability of the chelating agent citric acid in restraining the fast growth of nanoparticles in the carbon matrix,metal-oxide nanoparticles that are trapped in the carbon matrix and partially exposed to the pore channels which have been created.The main advantage of these supports is the formation of reducing iron species that are easily carbonization and forming a stable single-phase iron carbide.By adjusting citric acid amount and activation conditions,the size of?-Fe₅C₂ nanoparticles is readily tunable from 3.5 to 60 nm.And the formation of?-Fe₅C₂ have no relationship with the initial phase of Fe,and Fe nanoparticles with small particle diameters are easier to carry out rapid carbonization.