Hydrocarbon Synthesis from Carbon Dioxide and Hydrogen: A Two-Step Process

CO2 hydrogenation to olefins and ethylene oligomerization were investigated in efforts to improve catalyst composition and reaction conditions needed for scale-up. The hydrogenation of CO2 to hydrocarbons is investigated over γ-alumina-supported iron-based catalysts modified with manganese and potassium promoters and a silica-stabilized coating under fixed-bed reactor conditions to produce unsaturated hydrocarbons as feedstock chemicals for jet fuel synthesis. The stabilizer is introduced by impregnating the K/Mn/Fe on Al2O3 catalyst with tetraethylorthosilicate (TEOS) to minimize the deactivating effects of water on catalyst activity in CO2 hydrogenation. The K/Mn/Fe on Al2O3 catalyst modified with the TEOS and reduced in CO produced a lighter end fraction of olefins compared to the catalyst reduced in H2. To increase the chain length of the olefins formed in the CO2 hydrogenation step, investigation of the oligomerization reaction is conducted in a separate experiment, where pure ethylene is used as a model olefin. Ethylene oligomerization over pelletized amorphous silica–alumina (ASA)-supported Ni catalysts demonstrated high conversion and selectivity toward the jet fuel fraction (C8–C16) at a very low mass hourly space velocity (MHSV).