N₂ fixation, a process that transforms N₂ into biologically usable forms, is mainly accomplished by biological and industrial processes, respectively. Biological N₂ fixation is carried out by nitrogenase at ambient conditions. Coupled to the hydrolysis of ATP and accompanied by the formation of H₂, N₂ is reduced to NH₃. Industrial N₂ fixation is accomplished by Haber-Bosch process, in which N₂ is reduced to NH₃ efficiently in the presence of iron catalyst and promoter. The process invented more than a century ago is carried out at high temperature and high pressure(400~500 ℃, above 100 atm), which consumes lots of energy, in addition to the large amount of energy consumed in methanol steam reforming to produce hydrogen. Nowadays, people are looking for the next-generation industrial catalyst by taking inspiration from N₂ fixation mechanism of nitrogenase. Light-driven(photocatalytic) N₂ fixation is very promising especially considering that energy for N₂ fixation is ultimately from photosynthesis. In this paper, the recent progress in the field of bioinspired photocatalytic N₂ fixation in addition to some research on electrocatalytic N₂ fixation are summarized. Last, our perspectives of this field are provided. Although currently there is still no good substitution for catalyst system used in conventional Haber-Bosch process, a review of research progress and experience will provide beneficial implications for future design of efficient catalysts.
Contents
1 Introduction
2 Biological N₂ fixation and nitrogenase
2.1 Biological N₂ fixation
2.2 N₂ fixing mechanism and inspiration of nitrogenase
2.3 Transition metal complex for catalytic N₂ fixation
3 Photocatalytic N₂ fixation
3.1 Mechanism of photocatalytic N₂ fixation
3.2 Synthetic N₂ fixing photocatalysts
3.3 Biological hybrids and nitrogenase simulated photocatalysts
3.4 Overview of electrocatalytic N₂ fixation
4 Conclusion and outlook