Abstract

Ammonia synthesis, the conversion of inert dinitrogen (N₂) to ammonia (NH₃) is a process of fundamental biological and economic importance. The reverse reaction, ammonia decomposition, has recently attracted increased attention as a carbon-free hydrogen source. In order to design advanced catalysts that will be essential for a sustainable energy economy, an in-depth understanding of both the biological and chemical mechanisms is required. The focus of my research group is on the development and application of advanced spectroscopic tools, which allow for a detailed description of the atomic level processes in the both the biological and the heterogeneous systems. Specifically, a range of X-ray-based spectroscopic methods is utilized as a unique probe of transition metal active sites in complex media. High-resolution X-ray absorption spectroscopy (HERFD XAS), X-ray emission spectroscopy (XES), X-ray magnetic circular dichroism (XMCD), nuclear resonant vibrational spectroscopy (NRVS) and near ambient pressure X-ray photoemission spectroscopy (NAP-XPS) are utilized in combination with EPR, FTIR and Mössbauer. These experiments are correlated to advanced quantum chemical calculations to obtain a detailed picture of the electronic structure of the catalytic systems. Recent advances in our understanding of the nitrogenase enzyme and iron-based ammonia synthesis (and decomposition) catalysts will be presented.