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ERC

N2RED Report Summary

Project ID: 615414
Funded under: FP7-IDEAS-ERC
Country: Germany

Mid-Term Report Summary - N2RED (Spectroscopic Studies of N2 Reduction: From Biological to Heterogeneous Catalysis)

The conversion of dinitrogen to ammonia is a process of fundamental biological, ecological and economic importance. Presently, ~50% of the world’s ammonia is produced by bacteria containing the enzyme nitrogenase, while the other half is produced industrially using heterogeneous catalysts in the Haber-Bosch process. While both the biological and the enzymatic processes for ammonia synthesis are very efficient, the two processes operate at very different thermodynamic limits. The enzymatic system functions at ambient temperature and pressures, while the industrial catalyst requires both high temperatures and pressures. Ultimately, toward the broader goal of knowledge-based catalytic design, one would like to understand the differences in the biological and industrial process on an atomic level. This requires a detailed understanding of the geometric and electronic structural changes that occur in the catalyst over the course of a reaction. To this end, we are interested in developing and applying novel X-ray spectroscopic approaches that can be applied to both biological and heterogeneous ammonia synthesis catalysts. One such method we are developing is ligand selective X-ray absorption spectroscopy (XAS). This approach combines valence X-ray emission (XES), with XAS, in order to obtain selective K-edge data for a given metal-ligand interaction. This thus allows us, for instance, to select only for a specific Fe-N(nitride) interaction from a complex mixture of species. This approach has already been applied to nitrogenase, as well as to the iron-based heterogeneous catalysts used industrially. To date, we have focused largely on ex situ measurements, and in the next stage of the grant, we will focus on applications in situ. In addition to ligand selective XAS, we have also applied nuclear resonant vibrational spectroscopy (NRVS), X-ray Raman spectroscopy (XRS), X-ray magnetic circular dichroism (XMCD) and various resonant and non-resonant XES approaches. The experimental data have been correlated to theory allowing for a detailed understanding of the electronic structural changes that occur in the catalysts. This combination of methods has been used to obtain insight into the differences between vanadium- and molybdenum-dependent nitrogenases, where the former also enables Fishcer-Tropsch-like chemistry by being able to effect C-C bond couplings. Further, we have completed the design and construction of an in-house XES instrument. This instrument has allowed for both iron and potassium emission to be measured on iron heterogeneous catalysts. We expect the results of these combined studies should deepen our understanding of how the biological catalyst and the industrial catalysts activate the triple bond of dinitrogen, thus providing a path toward rational catalytic design.

Reported by

MAX PLANCK GESELLSCHAFT ZUR FOERDERUNG DER WISSENSCHAFTEN E.V.
Germany
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