Study On The Preparation Of Iron-based Nitrides And Their Catalytic Performance In Ammonia Decomposition

Ammonia(NH3)is an ideal hydrogen carrier,which has the advantages of high hydrogen storage density,easy liquefaction.Consequently,NH3 decomposition to provide COx-free hydrogen for fuel cell applications has drawn a great deal of attention.According to recent research,Ru-based catalyst possesses excellent catalytic activity and stability for NH3 decomposition.However,its expense and scarcity make it prohibitive for large-scale commercialization.Thus,alternative catalysts based on cheaper metals should be exploited.Transition metal iron oxide and nitride nanomaterials have many potential applieations in the fields of NH3 decomposition,electrochemistry due to the high catalytic activity,mild preparation conditions,simple operation and low cost.Therefore,it is realistic to study and develop effective Fe-based catalyst.The supported metal nanoparticle catalysts are widely used in heterogeneous reactions and play an important role in the field of industrial related reactions.In this work,the supported iron nitride catalysts were prepared by liquid phase reduction,conventional impregnation and in situ ammonia activation method.The activation temperature,gas and content of iron were investigated to find determine the optimum preparation conditions.The morphology,structure and element composition of the catalysts were characterized by transmission electron microscopy(TEM),X-ray powder diffraction(XRD)and X-ray electron spectroscopy(XPS).The results showed that the best low-temperature amnonia decomposition catalytic activity occurred with an iron content of about 10%and activation temperature of 500? in our reaction system.The synergetic effect of the active metal and the carbon nano tubes also has an effect on the catalytic activity.In addition,when subjected to high temperature reaction conditon,the metal particles of the catalyst showed no clear aggregation due to the confination effect of the carbon tube.Transition metal oxide nanomaterials have significant application value due to their nano-size effect and surface effect.And the transitional metal nitride catalysts based on metal oxides certainly have practical importance.In this paper,Fe2O3 with different morphologies and exposure of specific catalytic active faces were prepared by hydrothermal synthesis method and Fe2N catalysts with regular morphology were formed by in situ nitriding of Fe2O3 in ammonia flow.By high angle annular dark field scanning transmission electron microscopy(HAADF-STEM)and other characterizations,we concluded that the rod Fe2O3 exposes more high-index active crystal faces,after nitridation,the formed nitride species exhibited unique catalytic efficiency and stability compared with the cubic and discotic iron nitrides.Based on the one-component iron nitride catalyst,iron nitride-ruthenium bimetallic catalyst was constructed by in situ nitriding of the sample which Ru nanoparticles were evenly distributed on Fe2O3 and the bimetallic synergistic effect was discussed.To further improve the efficiency of the catalyst,the electronic additive lithium(Li)was incorporated into the catalyst and the mechanism of additive and active metal in ammonia decomposition was studied.As exhibited from the results,the bimetallic synergistic effect of the catalyst not only showed excellent catalytic activity,but also had better catalytic stability.