The Prepration And Microstructure Analysis Of Fe_1-xO Catalyst For Ammonia Synthesis

Ammonia synthesis is one of the key industries with high energy consumption.Therefore,it is of great significance to develop catalysts with high activities at low temperatures and low pressures.Iron-based ammonia synthesis catalysts are a novel catalyst system,with the great potential of further improvement.However,research of fused iron catalyst mainly is focused on the study of promoter optimization.The present work mainly centers around the effect of preparation method on the permance of catalysts for ammonia synthesis.In addition,the effect of novel promoter niobium oxide is investigated.In situ XRD technique is adopted for the eclucidation of catalyst reduction performance.The major results obtained are as follow.1.With L₈?2⁷? orthogonal experiment,during catalyst preparation,the effect feeding order of promoters on the performance of catalyst for ammonia synthesis was explored.The results shows that it is beneficial for catalyst feeding the promoters with high melting points with magnetite together,such as Al2O3,K2 O,Ca O,while the volstive promoters such as V2O5,WO3 are most suitable to be introduced to the molten liquid later.The catalysts prepared with stepwise addition of promoters in the order of alkaline to acid have higher activities than those catalysts with promoter addition in the order of acid to alkaline.2.The reduction performance of Fe_1-xO is facilitated ignificantly following the dopping of niobium oxide.Within the range of 0⁰.6wt%,it increases with niobium content.Furthermore,With niobium content of 0.6wt%,the catalyst possesses the highest activity for ammonia synthesis.3.Reduction and disproportionation reaction of Fe_1-xO catalyst was investigated by in situ XRD.The results show that the reduction temperatures of ZA-5 are between 325 ? to 415 ? in pure hydrogen atmosphere.The cumulative amonnt of active phase ?-Fe was calculated by the scherrer formula in the reduction process at different temperature.According to the cumulation during the reduction process,reduction of ZA-5 can be divided into three stages: induction period,acceleration period and decaying period.Disproportionation reaction of ZA-5 occurs at temperatures between 270 ? to 480 ? in Ar atmosphere.At temperature above 480 ?,the disproportionation ratio basically keeps unchanged,namely 32%.