Research Of Ammonia Synthesis Over Ruthenium Catalyst On N-doped Activated Carbon

Activated carbon supported ruthenium based catalyst is the second generation of new ammonia synthesis catalyst,which plays an important role in improving the ammonia synthesis activity and reducing industrial energy consumption.As the catalyst support,activated carbon material has many characteristics of good mechanical strength,pore structure,relatively large specific surface area and stable chemical properties,which the other oxides or carbon nanotubes do not have.Basically,the modification of activated carbon has influence in the activity and stability of the catalyst,and it is one of the most common ways to change functional groups on the surface of activated carbon.In this paper,we discuss nitrogen growing in situ on the surface of activated carbon and C3N4 as the support of catalyst,exploring the preparation method,comparing the impacts of different precursors to study the support itself and the catalyst produced changes.The main characterization methods were XRD,EA,XPS,TEM,FT-IR,physical adsorption,and chemical programmed reduction.The main conclusions are as follows:In the study of the precursors and doping temperatures,it was found that the nitrogen doping amount of N-doped activated carbon was directly related to the nitrogen content of the nitrogen precursor and quality of the precursor.The calcination temperature has a great influence on the doping amount of activated carbon.With the rising of calcination temperature,the nitrogen groups gradually decompose and the doping content decreases.Pyrrolic nitrogen and quaternary nitrogen are relatively stable.Because of that,the majority of nitrogen-containing groups are pyidinic nitrogen,which gradually decompose and tranform into the other two types of nitrogen with the temperature rising.With the introducting of more defects on the surface of the activated carbon,the ruthenium supporting sites are reduced.In this situation,the ruthenium particle size becomes larger,and the ruthenium precursor is reduced at lower temperature.The export concentration of ammonia synthesis under ruthenium-based catalyst supported by N-doped activated carbon at 800? was 20.80%.When nitrogen was used as nitrogen precursor to prepare N-doped activated carbon,addition of glucose can increase the nitrogen doping amount and the proportion of quaternary nitrogen,and the doping amount was proportional to the amount of glucose added.When the ratio of urea:glucose:activated carbon is 5:1:2,the supported graphite was nearly 40%,which catalyst supported by rearch 22.93%of ammonia synthesis.With the development of the surrounding electron density by quaternary nitrogen,ruthenium provides electrons to promote the dissociation of N2.Doping nitrogen will reduce the activation energy of catalytic reaction of ammonia synthesis,which is beneficial to the rising of reaction rate.In the preparation of g-C3N4,we can get the sample with the more surface area by using urea as a precursor instead of melamine.Also raising the temperature can improve the surface area of the material.The material of g-C3N4 has good thermal stability both in the air or nitrogen atmosphere,starting to decompose at the temperature of 550 ?.In the activity test,the catalyst with carbon nitride as the support exhibits better activity than the oxide support at low temperature because the basicity of C3N4 is stronger and the nitrogen content on the surface enhances the electrons of the supporting material performance.The strength of g-C3N4 is poor,which decompose into powder in the high pressure and leading to catalyst deactivation.