3.1 K2O Content Increased
K2O is one kind of Electrical Additives, it can increase the specific activity of catalyst. In the process of preparing catalyst, K2O and magnetite or other type additives reaction get sylvine, after reduction is evenly distributed on the surface of α-Fe, reduced the electrical work function on the surface of Iron, promoted the desorption and adsorption for ammonia. TA201-2 K2O content about 20% ~ 20% higher than that of other types of catalyst, it is one reason for TA201-2 has higher activity.
3.2 Adding cobalt oxide to improve the catalyst activity
TA201-2 is one kind of double active component of iron cobalt catalyst. In the process of melting, cobalt oxide and magnetite forms solid. After the reduction, cobalt atoms uniformly distributed in the α-Fe, which decreases the α-Fe significantly, lattice distortion, promotes more [111] face to expose, increases the number of active center, and improves the pore structure, increase 40 ~ 70A0 micropore. It is benefit to the transfer of reactants and products. Type TA201-2 ammonia synthesis catalyst contains a certain amount of CO3O4,, which makes it have good low temperature activity.
3.3 Adjust the content of Al2O3 and CaO additives
Al2O3 and CaO are structural additives. In the process of melting, they form solid solution with magnetite, metal ions into the spinel structure of oxygen ions of closest packing is tetrahedral and octahedral gap, making them evenly distributed among the magnetite. In the process of reduction and use, these oxide can not be restored with function of isolation of alpha Fe, making the grain size and stability, improving the catalyst activity and stability. on the other hand, ammonia synthesis make a number of catalytic reaction on molten iron catalyst. The dissociation and synthetic reaction of H2N2 molecule adsorption are conducted in alpha Fe grain on the surface. Analysis shows that the surface structure, iron surface area occupy some percent of the entire surface area of catalyst. Most of the surface is occupied by oxide additives without reduction. Therefore, some documents think, on the basis of not affecting lifetime, we can decrease additives to improve the catalytic performance.TA201-2 fully considers the combination of structural auxiliaries, reasonably adjust the content of Al2O3 and CaO additives. It is great to improve the activity of catalyst and to improve the catalyst reduction performance. Compared with other type catalyst, TA201-2 reduce the content of Al2O3 and CaO dramatically.
Form 3 Portion of Al2O3 and CaO content in ammonia synthesis catalyst
| Type
Content of additives |
TA201-2 |
A110 |
A |
B |
C |
| Al2O3% |
1.30 |
2.60 |
2.25 |
1.95 |
2.40 |
| Relatively content |
100 |
200 |
173 |
150 |
185 |
| CaO% |
0.80 |
2.20 |
1.40 |
1.78 |
1.60 |
| Relatively content |
100 |
275 |
175 |
225 |
200 |
| K2O% |
0.87 |
0.60 |
0.58 |
0.52 |
0.70 |
| Relatively content |
100 |
75 |
72 |
65 |
88 |
3.4 Adding a special additives to improve the catalyst thermal stability
It is generally recognized that reducing the content of Al2O3 and CaO can be advantageous to the catalyst activity increase and makes the catalyst easy to restore. But its thermal stability will be reduced. To make up for the shortcomings, we work through a large number of screening, add a special additives. It can effectively prevent gathered in potassium ion transfer to the inside catalyst particles on the surface of the catalyst, making the potassium ions on the surface of catalyst residence time longer. Then it will greatly improve the thermal stability and service life of the catalyst. Using the additives can first combine with poison (mainly CO and CO2)and can release under high H2, therefore, to a certain extent, it can enhance the poison resistance of the catalyst.
3.5 The choice of Fe2 + / Fe3
Fe2 / Fe3 + is a key indicator of molten iron catalysts. There are a few research reports at home and abroad about the influence of the ratio of iron for catalytic performance. Usually Think that the ratio of iron has the best catalytic activity controlling the number in 0.50~0.60. We think that, there are different choices for the best ratio of iron as for adding different types and contents of additives. In the process of research and development of Type TA201-2 ammonia synthesis catalyst, we made research on the influence of ratio of iron for the reducing property, catalytic activity, thermal stability, and mechanical strength of catalyst. Compared with other catalyst,ratio of iron of Type TA201-2 ammonia synthesis catalyst is the lowest. This is good for Al2O3 metal ions to enter into the spinel structure, making them evenly distributed in the magnetite phase, giving full play to the structure of Al2O3 fertilizer effect. Therefore, although TA201-2 Al2O3 content in the catalyst decreased obviously, adjusting the ratio and adding some special additives of iron make it still has good thermal stability. Laboratory performance test results and factory usage practice also confirmed the related view.
Form 4 Portion Ammonia Synthesis Catalyst Fe2+/Fe3
| Type
Iron Proportion |
TA201-2 |
A110 |
A |
B |
C |
| Fe2+/Fe3+ |
0.35~0.45 |
0.50~0.60 |
0.68 |
0.45~0.60 |
0.50~0.60 |
Noted: A、B、C is the same type ammonia synthesis catalyst in domestic