Natural Sources of Fixed Nitrogen

Apart from minor sources such as thunderstorms (Section 9.2), atmospheric nitrogen is fixed in Nature by certain soil bacteria, blue-green algae, and microorganisms in the root nodules of legumes. This is accomplished either by oxidation to nitrate 

Reaction 9.1 might seem to be thermodynamically favored, but in fact no kinetically easy route from triply bonded N2 to N03 exists, since the endothermic intermediate NO (Section 8.4.2) is likely to be involved. As written, reaction 9.2 has prohibitive energetics, but in practice the process is more complex than this. For example, the fact that free O2 is not formed, but is in effect consumed in other biochemical reactions, makes for a favorable energy balance. The limiting factor is again kinetics, as plausible intermediates such as hydrazine (H2N—NH2) are endergonic compounds. 

The prospect of mimicking the ability of nitrogenases to fix N2 in mild aqueous conditions is attractive in view of the high energy and capital 

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