PhD Defence by Simon Ingeman Hansen

Principal supervisor
Associate Professor Jakob Munkholt Christensen
DTU Chemical Engineering

Co-supervisor:
Professor Anker Degn Jensen
DTU Chemical Engineering

Examiners:
Associate Professor Martin Høj
DTU Chemical Engineering (chairman)

Professor Martin Muhler
Ruhr University Bochum, Germany

Head of e-Chemicals and Synthesis Technology Per Aggerholm Sørensen
Topsoe

Chairperson at defence:
Senior researcher Brian Brun Hansen, DTU Chemical Engineering

Popular summary

The industrial synthesis of ammonia from its elements has been described as the most important invention of the twentieth century and provides artificial fertilizer that sustains half
of the global food supply. Hence, the synthesis of ammonia is essential, but it is also a very energy intensive process. Currently, the global ammonia production is approximately 180
million tons annually consuming around 1.8 % of the global energy output each year. This causes a significant release of CO2 constituting approximately 1 % of the world’s total carbon
emissions. Moreover, new applications for ammonia are emerging, such as using ammonia as a marine fuel or energy carrier in Power-to-X. It is therefore clear that research within
catalytic ammonia synthesis remains highly relevant as the demand for ammonia is only expected to grow.

The catalytic synthesis of ammonia is one of the most studied chemical reactions and is often referred to as the bellwether reaction in heterogeneous catalysis. Despite being labeled
as the bellwether reaction, catalytic ammonia synthesis has not been fully understood. Thus, research in catalytic ammonia synthesis continues on a fundamental level, which will benefit
industrial applications. Currently, the dissociative adsorption of nitrogen is widely considered to be the rate-determining step, but studies have shown that the rate of nitrogen uptake on
the catalyst surface is accelerated by the presence of hydrogen.

In this thesis, the reaction mechanism of catalytic ammonia synthesis was investigated in detail through isotope exchange studies. Moreover, the importance of gas purity in catalytic
ammonia synthesis was illuminated and a new protocol was established to ensure sufficient gas purity to warrant reproducible results. Lastly, a new adsorption isotherm was proposed,
providing an improved description of adsorption phenomena, which is not only relevant in the field of catalysts, but also across a range of other scientific fields such as enzyme
immobilization and transmission of viruses via solid surfaces.