Beyond fossil fuel-driven nitrogen transformations

Abstract

Nitrogen is fundamental to all of life and many industrial processes. The interchange of nitrogen oxidation states in the industrial production of ammonia, nitric acid, and other commodity chemicals is largely powered by fossil fuels. A key goal of contemporary research in the field of nitrogen chemistry is to minimize the use of fossil fuels by developing more efficient heterogeneous, homogeneous, photo-, and electrocatalytic processes or by adapting the enzymatic processes underlying the natural nitrogen cycle. These approaches, as well as the challenges involved, are discussed in this Review.

Figure 1.

Atom and energy economy of nitrogen fixation. The numerical values represent standard (for gaseous reactants and products and liquid H₂O, as defined in ref. 14) Gibbs free energies in kJ/mol of fixed N₂ in the direction of the arrows. All thermochemical data are from ref. , except for H₂NOH (ref. 16).

Figure 2.

Linear scaling between nitrogen binding energy and activation barrier for N₂ dissociation. TOF = turnover frequency (from ref. 22).

Figure 3.

FeMo-cofactor with Fe in rust, S in yellow, C in gray, Mo in magenta, and O in red. Made from PDB: 1M1N

Figure 4.

Partial Pourbaix diagram for the N₂-H₂O system showing lines corresponding to N₂ reduction to NH₄⁺/NH₃ and N₂ oxidation to NO₃⁻ . Lines a and b straddle the region of water stability (reduction to H₂ and oxidation to O₂, respectively). See ref. for details and refs. 15 and 19 for primary data.