Exprolation And Optimization Of Promoters Of Fe_1-xO Based Catalysts For Ammonia Synthesis

Ammonia synthesis is one of the industries which consume huge energy.Therefore,research and development of high activity and stability catalysts with high ammonia net value and low energy consumption process are the key issues.Fused iron catalyst is considered as one of the most stable and the cheapest catalyst among all industrial catalysts,and its preparation is also simple.Fe1-xO based catalyst is a new catalyst system for ammonia synthesis,with high potential for improvement.At present,research on fused iron catalyst is mainly focused on the study of promoters.Hence,based on the existed results of previous studies,the exprolation and optimization of new promoters is the most possible way to improve the performance of Fe1-x,O catalyst.In this thesis,the composition of Fe1-xO catalysts is optimized and several novel promoters are investigated in detail.In addition,the catalyst preparation procedure is studied.Finally,the computation about the adsorption of electronic promoter K2O on alpha Fe is carried out by the density functional theory.The following results are obtained:1.Promoter M1 enhances the activity of Fe1-xO based catalyst significantly.Under the conditions studied,the activity is increased by 4.93%and 6.84%at 425? and 400? respectively.M2 reduces the reduction procedure significantly,and the reduction temperature of the catalyst is much lower than the catalyst without M2.Both M1 and M2 improve the specific surface area and pore volume of Fe1-xO based catalysts.0.2wt%R improves the activity at the low temperatures,but reduces the heat stability of the catalyst,while A can not improve the activity of the catalyst,but it improves the reduction procedure.2.With L8(23)orthogonal experiment,the contents of classical promoters Al2O3,K2O,CaO are optimized.The results show that there is strong interaction between Al2O3 and K20 on the thermal stability of catalyst.The optimal portfolio is 1.53wt%Al2O3,0.7wt%K20,1.8wt%CaO,and it is confirmed by separate experiments.3.The effects of MgO and J on catalyst activity were investigated with L4(23)orthogonal experiment.The results indicate that MgO improves the activity but not for J.There is no interaction between MgO and J.4.With L8(23)orthogonal experiment,the suitable contents of L,M1,Q,and their interaction were studied.The results prove that there is strong interaction between M1 and Q on the thermal stability.Considering the activity of catalysts at 400?,425 ?,450? and the heat coefficient,the orthogonal optimal portfolio is 0.42wt%L,0.89wt%M1,0.6wt%Q.5.With L8(23)orthogonal experiment,the study about the effect of M2,Z and X on the performance of catalysts was carried out.Considering the activity and the heat coefficient,the orthogonal optimal portfolio is 0.3wt%M2,0.4wt%Z,Owt%X.Unlike the ruslts of traditional Fe3O4 based catalyst,X can't improve the activity of Fe1-xO based catalyst.6.During the preparion of fused iron catalyst,bubbling the molten material into water jacketed cooling trough is confirmed to be the most propriate route for cooling.Purity of raw materials influences the activity of catalysts.Higher than 0.85wt%impurity of Na2O in the catalyst reduces the catalyst activity by 31%.The forms of promoter metals(replacing M1 with its ammonium salt)have no noticeable effects on the activity.7.Adsorption of K20 on Fe(100)and Fe(111)surface tends to take place on hollow position,but for Fe(110)it tends to be the top bit(on top).The interaction between K20 and Fe(111)crystal plane is the strongest among all the Fe planes.Electronic state density calculation results of K20 adsorpted on Fe(111)surface show that charge transfer happens in the adsorption system.To some extent,it explains the electronic help of K20 in fused iron catalyst for ammonia catalyst.