Mechanism of ammonia synthesis

Studies of the Kinetics and Mechanisms of Ammonia Synthesis and Hydrodesulfurization on Metal Single-Crystal Surfaces... 

Many works were devoted to the mechanism and kinetics of ammonia synthesis. In accordance with the outline of this article, only the main results of studies of ammonia synthesis by the author with co-workers will be presented here other works will be cited, but in connection with our studies. The discussions of kinetics and the mechanism of ammonia synthesis in the reviews published in this series (90) and in the contribution by Nielsen et al. (91) can serve as supplementary sources of information. The contribution by Malina (92) contains interesting historical data and an extensive list of references. 

Thus, here we have two independent routes. For a linear mechanism of ammonia synthesis on an iron catalyst we will have... 

A. Ozaki, K. Aika Catalytic Activadon of Dinitrogen The third chapter is a comprehensive and critical review of studies on the catalytic activation of dinitrogen, including chemisorption and coordination of dinitrogen, kinetics and mechanism of ammonia synthesis, chemical and instrumental characterization of active catalysts, and homogeneous activation of dinitrogen including metal complexes (353 references). 

Table 7.3.1 CHAPTER 7 ivncroKineTic Analysis nr e.aiaiyiic Heantinn< 1 A proposed mechanism of ammonia synthesis over iron catalysts. ig /... 

The most famous example of the application of the concept of ninuniformity in catalytic kinetics is the mechanism of ammonia synthesis. Schematically, in the simplest treatment, the ammonia synthesis mechanism near equilibrium was pictured in the following way... 

Figure 7.26. The activation energy for ammonia synthesis on Fe(lll) and K/Fe(lll). Within experimental error there is no change, suggesting that potassium does not change the reaction mechanism of ammonia synthesis [59].

J G. Ertl. Surface Science and Catalysis—Studies on the Mechanism of Ammonia Synthesis The P.H. Emmett Award Address. Catal. Rev. Sci. Eng. 21 201 (1980). 

Extensive investigations of the mechanism of ammonia synthesis have shown that the rate-determining step is the dissociation of coordinatively bound nitrogen molecules on the catalyst surface. Hydrogen is much more readily dissociated on the catalyst surface. The adsorbed species then undergo a series of insertion steps, in which ammonia is formed stepwise and is finally desorbed (Scheme 8-1). 

The study on the pattern of nitrogen chemisorption is very important for the understanding of reaction mechanism of ammonia synthesis. But the chemisorption of nitrogen on the surface of transient metals is very complex. Taking chemisorption on iron catalyst for ammonia synthesis as an example, it was found that the formation rate of ammonia depends on pre-adsorption temperature if the adsorption of nitrogen was preceded first on the surface of activated catalyst, and then hydrogen was passed on surface of pre-adsorbed nitrogen. It is considered that there exist two adsorption patterns The first one is of L-type which appeared at 200°C of pre-adsorption temperature, in which the formation rate of ammonia was proportional to second one is of H-type which appeared at 400°C 40°C of... 

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