PhD defence: Bifunctional Catalysis to convert Synthesis Gas to Chemicals and Fuels

To fulfill the demand for chemicals and fuels in combination with a growing world population, an alternative to fossil feedstock must be found to circumvent the potentially catastrophic consequences of climate change. Synthesis gas, a mixture of hydrogen, carbon monoxide and/or carbon dioxide, can be derived from more renewable sources, such as municipal waste and biomass. Fischer-Tropsch catalysts convert synthesis gas to intermediate molecules which can further react to chemicals, such as olefins or aromatics, or to fuels, such as gasoline or diesel, over zeolite catalysts. This thesis addresses the combination of iron-based Fischer-Tropsch catalysts with zeolites in so-called bifunctional catalysts. These catalysts allow to convert synthesis gas to chemicals and fuels in a single reactor.

By the addition of certain compounds (so-called promoters) to a Fischer-Tropsch catalyst the catalytic performance can be increased significantly. It was found that these promoters located on the Fischer-Tropsch catalyst can migrate to the zeolite during the conversion of synthesis gas to aromatics, which causes the catalytic performance of the promoted Fischer-Tropsch catalyst to deteriorate over time. This was shown by a detailed analysis of the catalyst performance as well as by advanced spectroscopic methods. Furthermore, well-defined iron nanoparticles were prepared and further attached to zeolite crystals in order to synthesize bifunctional catalysts. The synthesis method to introduce the promoters for the Fischer-Tropsch catalyst plays a crucial role for the performance and stability of the bifunctional catalyst. During the conversion of synthesis gas to gasoline the reactions of bond-making and -breaking of intermediate products were followed along the catalyst bed.