Nanocatalysts from Ionic Liquid Precursors for CO2 Valorisation to Hydrocarbons

The conversion of CO2 into lower olefins (C3-C5) is a highly desirable process as a sustainable production route. Thereby, the use of hydrogen from renewable energies and the conversion of CO2 into lower olefins via Fischer-Tropsch synthesis (FTS) offers an attractive route for efficient utilisation of biogas as a renewable feedstock to replace petroleum for the synthesis of key building-block chemicals. Lower olefins, i.e., ethylene, propylene and butene (C2-C4) are key building blocks in the current chemical industry. Iron-based catalysts are of interest due to their ability to catalyse both FTS and Reverse Water Gas Shift (RGS). These are also of interest as they are able to produce high olefin hydrocarbons. The main reason for the iron catalyst effectiveness in such process is its formation of iron carbides (χ-Fe5C2) formed after reaction gas treatment. It has also been reported that the iron catalysts require alkali metal promotion in order to obtain desired activity and selectivity. The further upgrading to gasoline range hydrocarbons can be done by having zeolites in close proximity to the iron catalysts. It has been proposed that the zeolites crack lower chain olefins, and able to facilitate chain growth.However, for such catalysts, controlling the size and the particle distribution remains a major challenge. Thus, in order to obtain monodispersed catalysts, a novel approach is developed, utilising ionic liquids which can dissolve precursors while itself containing dense and tuneable network of hydrogen bonds. Such synthetic methods have been demonstrated by Wang et al. Nanoparticles produced through this method have been shown to produce higher surface areas. We report here on a novel methodology for the controlled synthesis of a Na–Fe3O4/HZSM-5 multifunctional catalyst for the direct hydrogenation of CO2 to gasoline. The catalytic testing under industrially relevant conditions resulted in improved selectivity to C5–C11 as well as low CH4 and CO2 selectivity. Furthermore, the product composition can be tuned by the zeolite properties (i.e. Si/Al ratio, H form, alkaline exchange) and by the choice of ionic liquid in the synthetic method. This study provides a new pathway for the synthesis of nanocatalysts for the production of liquid fuels by utilising CO2 and H2.