Molecular Simulation On Preparntion Of Fischer-tropsch Synthesis Iron-based Catalyst

Fischer-Tropsch synthesis conversion efficiency and product selectivity are closely related to catalyst performance.Among them,iron-based catalysts have been attracting attention as an early catalyst for Fischer-Tropsch synthesis research because of their abundant reserves and low prices.The synthesis of highly efficient iron-based catalysts focuses on the preparation of precursors.However,due to the complicated experimental environment of the preparation process,it is difficult to analyze by conventional means.Therefore,this paper uses molecular simulation to analyze the preparation process of Fischer-Tropsch synthesized iron-based catalyst precursors.Starting from iron ions,two processes from iron ions to hydrated iron ions and from water and iron ions to Fischer-Tropsch iron-based catalyst precursors were studied.Using molecular simulation methods,a series of properties and changes including thermodynamics were analyzed.Firstly,according to the ligand and coordination number of hydrated iron ions,the energy minimum structure of[Fe(OH)_n]^3-n(1?6)and[Fe(H₂O)_n]³⁺(1?6)was established.Type,and studied the conversion relationship between different hydrated iron ions.It is found that with the increase of PH,the hydrated iron ions will deprotonate,the ligand of iron ions will be converted from water molecules to hydroxide,and when three protons are removed,the water molecule ligand will be completely converted into hydrogen and oxygen.Root ligand.Among them,the relatively stable hydrated iron ions are[Fe(OH)4]-and[Fe(OH)₆]^3-.Secondly,according to two relatively stable hydrated iron ions,the dehydration condensation process of hydrated iron ions was analyzed by density functional theory.It is found that the[Fe(OH)₄]^-structure is more prone to chain growth,and the[Fe(OH)₆]^3-structure is more prone to ring growth,especially the process of generating a three-membered ring is extremely thermodynamically advantageous..We calculated the nucleation path of hydrated iron ions by using the three-membered ring as the smallest structural unit.The synthesis process of the Fischer-Tropsch synthesis iron-based catalyst precursor hydroilite is mainly composed of a plane formed by the multi-directional path 1 with a 1:1 ferrite tetrahedron and a ferrite octahedron link.In addition,we also studied the molecular dynamics simulation of the precipitation process of hydrated iron ions in water.The precipitation process was studied by establishing molecular dynamics systems of different concentrations and sizes.The results show that iron ions will form hydrated iron ions with water molecules in water first,and the coordination number will gradually increase,and the deprotonation process will occur.The structure of dimers will be formed between multiple hydrated iron ions.The advancement gradually forms some small ring structures,which in turn form larger hydrated iron ion clusters,as well as the initial ferrite nucleus.