Deposition of Iron Oxide Nanoparticles onto an Oxidic Support Using a Novel Gas-Expanded Liquid Process to Produce Functional Fischer–Tropsch Synthesis Catalysts

Gas expanded liquids (GXL) are solvent systems which enable the controlled deposition of presynthesized iron oxide nanoparticles, based on their size, onto a surface through the use of compressible gas such as CO₂. By controlling the applied CO₂ pressure, and hence the solvent strength, one can systematically deposit/precipitate nanoparticles of desired sizes. In this study, a technique using a GXL has been developed to controllably deposit iron oxide nanoparticles onto oxidic materials such as alumina and silica. The nanomaterials generated using this technique were then tested for their effectiveness as catalysts in Fischer–Tropsch (FT) synthesis in a fixed bed reactor system under standard low temperature FT conditions. The catalytic performance of these nanoscale iron FT catalysts was compared to control catalysts that were prepared by traditional incipient wetness methods using the same iron loading. Characterization of these GXL-synthesized materials demonstrated that the iron oxide nanoparticles were deposited in a size controlled manner onto the oxidic support. A CO conversion of 18% was observed using a silica catalyst generated using this GXL technique along with a 69% selectivity toward C₅₊ hydrocarbons. The nanoscale iron catalysts prepared by the GXL technique employed in this study exhibit weaker interactions between the iron oxide nanoparticles and the support material, offering a new strategy to investigate the effect of metal–support interaction on the activity and selectivity of iron based FT synthesis catalysts