(350b) Preparation and Characterization of Fischer-Tropsch Active Co/SiO2 Catalyst Modified with a Chelating Agent

Fischer-Tropsch synthesis (FTS) is an alternative for the production of transportation fuels, chemicals, and other hydrocarbons through the catalytic conversion of syngas (CO and H₂). Cobalt based catalyst are favored over iron for synthesis of long-chain alkanes. The present study investigates the surface-structure characteristics and FTS activity of Co/SiO₂ catalysts. A solid-state reaction between cobalt and silica support could result in cobalt silicate formation, which does not catalyze FTS. Therefore, a strong interaction of cobalt with a support is undesired and must be minimized. In this study, two different chelating agents, nitrilotriacetic acid and ethylenediaminetetraacetic acid, were used to modify the support during incipient-wetness impregnation with cobalt nitrate. The physical characterization of catalysts was performed by XRD, XPS, TPR and N₂-adsorption. FTS was carried out in a fixed-bed reactor at 230°C, 2.0 MPa and 3Nl/gcat/h, using syngas with H₂/CO = 2.0. The operating conditions were selected to maximize diesel-range hydrocarbons (C₉-C₂₀). The presence of a Co₃O₄ phase was confirmed by the data from XRD studies. The average crystallite size of Co₃O₄ phase is in the range of 10 to 15 nm when calcined at 250°C. The reduction process of Co₃O₄ into metallic Co is shown to proceed in two steps, based on two strong peaks observed in TPR study. The addition of a chelating agent is shown to improve the surface concentration of cobalt on silica, as confirmed from intensities of Co2p peaks in XPS analysis. Finally, catalyst performance was evaluated based on selectivities towards C5⁺ hydrocarbons and CO conversions.