Study Of Ru-Fe Composite Catalyst For Ammonia Synthesis

Activated carbon supported Ru catalyst shows higher activity for ammonia synthesis than Fe-based catalysts.However,under operation conditions,Ru catalyzes the methanation of carbon support.In the present study,wustite-based iron catalyst(Fe_1-xO)developed by our lab was adopted as a novel carrier of Ru catalysts for ammonia synthesis.The factors affecting catalyst performance such as preparation methods,promoter content,ruthenium loading,treatment temperature were investigated in detail.Three methods including polyol reduction method,mechanical mixing and sublimation were used to prepare Ru/Fe_1-xO catalyst for ammonia synthesis.The effect of preparation methods and carrier treatments on catalyst activity,stability and dispersion of ruthenium were characterized by X ray diffraction（XRD）,scanning electron microscope（SEM-EDS）and thermogravimetric analysis（TG）.The following results were obtained:1.Ru/Fe_1-xO catalysts were prepared by sublimation route,and it was found that sublimation temperature,ruthenium loading,particle size of catalyst support,promoter content affect the catalytic activity.Fe_1-xO catalyst with particle size1.00-1.43cm is suitable for the loading of Tri-ruthenium dodecacarbonyl.In addition,the activity of catalyst increase with Ru loading before it drops at Ru loading of0.764%.The content of K and Ba with 2.5%and 0.5%respectively was found to be beneficial for the composite catalyst.The optimized preparation conditions of the composite catalyst were selected as sublimation temperature and time of 140℃and10h,heating rate of 4^oC/min.2.Ruthenium catalysts supported on the wustite-based iron catalyst(Fe_1-xO)was prepared via mechanical mixing with tri-ruthenium dodecacarbonyl as the Ru precursor.The results show that mechanical mixing is able to load ruthenium to wustite-based iron catalyst,and the activity was improved.The treatment temperature after mixing affects the activity of the catalyst.The change in the content of Ru loading play a significant role in the performance of catalyst as well as the treatment atmosphere.Relatively high activity was achieved with treatment temperature of120℃.With Ru loading varying from 0.2%to 2%,activity of catalyst firstly increases before it drops at Ru loading of 0.6%.3.Ruthenium nanoparticles was prepared by polyol reduction method using ruthenium（Ⅲ）chloride and sodium acetate as the Ru precursor and the stabilizer,respectively.Ru catalysts supported over Fe_1-xO catalyst were prepared via wet impregnation with Ru this suspension.Uniform Ru nanoparticles were achieved at temperature of 150℃,sodium acetate concentration of 0.03mol/L.However,activity of the composite catalyst was not improved significantly.In the process of preparation,the selection of washing solution and the promoters influence the activity of the catalyst.