Nitrogen fixation temperature

Like the Haber process for the synthesis of ammonia, this reaction represents a way of converting elemental nitrogen into a compound (nitrogen fixation). Moreover, calcium cyanamide reacts with steam at high temperature to yield ammonia,... 

A class of plants, called legumes, has bacteria which extract N2 directly, converting it to NH3. This nitrogen fixation process, catalyzed by an enzyme produced by the bacteria, is highly efficient at usual temperatures and pressures. 

Figure 4.23 Kinetics of nitrogen fixation with hydrogen peroxide molar ratio N2 30% H202 = 1 1.6 (1-3 T = 773, 823 and 873 K, respectively, and 4—6 theoretical curves at these temperatures).

Figure 5.12 shows temperature dependencies of final and intermediate product accumulation or consumption for N2 hydroperoxide oxidation. Fixed nitrogen concentration in the reaction mixture reaches the maximum at 873 K and then decreases with a temperature increase to 923 K. Flence, hydrogen peroxide concentration decreases abruptly, which is associated with its consumption in the target reaction of nitrogen fixation HO and OH radical concentrations sharply increase with temperature. 

The chemical unreactivity of the N=N bond is clearly seen when one considers the industrial process of nitrogen fixation. This process, devised by Fritz Haber in 1910 and still used today in fertilizer factories, involves the reduction of N2 in the presence of H2 gas over an iron catalyst at a temperature of 500°C and a pressure of 300 atmospheres. 

Other processes have been proposed for nitrogen fixation, but none of these have approached a commercially attractive stage. For example, it was shown that low energy ultraviolet photons can form nitric oxide at room temperature under oxidizing conditions on the surface of a titanium dioxide-containing material8. 

While the latter reactions are no longer used for nitrogen fixation, the reaction of dinitrogen with dihydrogen to form ammonia is among the most important industrial processes. The alkaline-earth metals react readily with dinitrogen at elevated temperatures to form nitrides lithium reacts even at room temperature with dinitrogen. 

Nitrogen fixation also results from the high-temperature combustion process in automobile engines. The nitrogen in the air is drawn into the engine and reacts at a significant rate with oxygen to form nitric oxide (NO), which... 

The only reactions of molecular nitrogen at ambient temperature are the formation of lithium nitride Li3N, reactions with certain transition metal complexes, and nitrogen fixation with nitrogenase in the bacteria of the root nodules of legumes and in blue algae (Sections 14.1.1 and 14.1.2). Above 500 °C nitrogen reacts with some elements, especially with metals (nitride formation). 

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