N2 Fixation by Plasma-Activated Processes

Nitrogen is fundamental to all of life and to many industrial processes. Nitrogen in its various oxidation states comprises the global nitrogen cycle, with the change between forms being redox reactions involving electrons and protons. The interchange of nitrogen oxidation states constitutes some of the most important industrial processes, with the energy for these processes being provided largely by fossil fuel. A key goal of research in the field of nitrogen chemistry is to minimize the use of fossil fuels by developing more efficient heterogeneous, homogeneous, or biological catalysts, or by inventing new energy-efficient processes that rely on catalysts. These approaches, as well as the challenges involved, are discussed in this review. This review article reports on the current state of the field of nitrogen activation chemistry and discusses future directions.

Ammonia is an important nutrient for the growth of plants. In industry, ammonia is produced by the energy expensive Haber-Bosch process where dihydrogen and dinitrogen form ammonia at a very high pressure and temperature. In principle one could also reduce dinitrogen upon addition of protons and electrons similar to the mechanism of ammonia production by nitrogenases. Recently, major breakthroughs have taken place in our understanding of biological fixation of dinitrogen, of molecular model systems that can reduce dinitrogen, and in the electrochemical reduction of dinitrogen at heterogeneous surfaces. Yet for efficient reduction of dinitrogen with protons and electrons major hurdles still have to be overcome. In this tutorial review we give an overview of the different catalytic systems, highlight the recent breakthroughs, pinpoint common grounds and discuss the bottlenecks and challenges in catalytic reduction of dinitrogen.