Preparation ammonia synthesis catalysts

Figure 6 Correlation between both N2 adsorption and NH3 production rates and the structure of the catal)dic surface, as determined hy studies with various single crystals of ironT These results explain the strong dependence of the performance of commercial ammonia synthesis catalysts on their method of preparation ...

Alwin Mittasch joined BASF in 1904 as a co-worker of Carl Bosch and started the search for suitable ammonia synthesis catalysts soon afterward. These efforts were considerably intensified after Haber s successful experiments but, at first, only with limited success. He mentioned (4) In particular iron failed, despite wide variations of the preparation conditions and admixtures. The breakthrough was obtained by accident A sample of Swedish magnetite left over from other experiments was investigated on November 6, 1909, by Mittasch s collaborator Dr. Wolf and exhibited remarkably high ammonia yields. The decisive patent application of January 9, 1910, says the following ... 

Bulk catalysts comprise mainly active substances, but some binder is often added to aid the forming/shaping operation. This is the case for iron oxide for the water-gas shift (WGS) reaction, iron molybdate for the oxidation of methanol to formaldehyde, and vanadyl pyrophosphate for butane oxidation to maleic anhydride. However, in some cases, bulk catalysts are used as prepared, without the need for addition of the binder. Typically, this involves catalysts prepared by high temperature fusion (eg, the iron-based ammonia synthesis catalyst). The need for the addition of binder, or the requirement for pelleting, solely depends on the strength required for the catalyst under the reaction conditions and the reactor type that is used in. This requires consideration of attrition resistance, and oxide... 

The value of tortuosity factor depends on the composition and preparation methods of catalysts. The values measmed for Fei xO-based A301 ammonia synthesis catalyst are Porosity 0 = 0.36, average radius of pore is 16 nm, and tortuosity factor is 3.28.230... 

The preparation conditions of each step significantly influence the physical properties and catalytic performance of the catalyst. The key steps for production of ammonia synthesis catalysts by melting method are the purification of raw materials, controlling of Fe +/Fe + ratio, and the cooling speed during the solidification process. 

The SEM of Ru-based ammonia synthesis catalyst prepared by isovolume-impregnation is shown in Fig. 6.28. It can be seen from Fig. 6.28 that the active components are dispersed on support in three ways (i) certain sized active component is dispersed on support unevenly (Fig. 6.28 (a)), (ii) Active component of atom-like state is dispersed on support in cluster (three-dimensional) or raft like (two-dimensional) (Fig. 6.28(b)). (iii) Active component is distributed on the support like accumulated snow (Fig. 6.28(c)), which is an amorphous phase amorphous phase by XRD analysis. Among them, sample 3 has the highest activity in which active component is accumulated like snow on the support after reduced with H2 at 200°C for 2h. The sample 1 and 2 are not reduced in H2 and are just dealt with in vacuum or dried at low temperatures. Their activities are lower, which are only 1/5 to 2/5 of sample 3. It can be seen that the reduction of catalyst with H2 is necessary during the preparation process. 

In summary, the precipitation-washing processes can be considered as the new method of preparing the efficient Ru based ammonia synthesis catalyst. It not only significantly increases the catal3dic activity, but also simplifies operation, decreases the complexity of the catalyst preparation technology, and reduces the... 

Zhang SJ, Preparation and Performance of New Ammonia Synthesis Catalyst, Dissertation, Fuzhou University. 

In the early research stages of ammonia synthesis catalyst, Mittasch et al. studied almost all metal elements and their bimetallic alloy in the Periodic Table. Several metals have no or less catal3dic functions themselves. However, the addition of some promoter could increase their activities. The addition of a secondary metal into Fe, Mo, W, Co, Ni, Pd, Pt, Os, Mn enhances their activities. The different ratio between two metals leads to a different activity. It can be concluded from these results that the addition of metals in Vlff or VI groups favors enhancing of iron-based catalyst activity. For example, Fe-Mo (1 1) catalyst has high activity. If the Mo content is less than 80%, the activity decreases after running for a long-time. These catalysts are prepared by calcinations of metal nitrates and ammonium molybdate... 

Liu et al. reported an ammonia synthesis catalyst prepared by using complex of tri-iron formic acid as precursor. The testing results showed that it had high activity. ... 

Jacobsen CJH, Blosen M, Seichst J, et al.. Preparation Method of Ammonia and Ammonia Synthesis Catalyst. CN 1266815A. 2000. 

PREPARATION AND ACTIVATION OF THE TECHNICAL AMMONIA SYNTHESIS CATALYST... 

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