Effect of support surface treatment on the synthesis, structure, and performance of Co/CNT Fischer–Tropsch catalysts

• Co/CNT were functionalized using gas-phase oxidation or used untreated.
• Co/CNT catalysts were prepared by incipient wetness impregnation using H2O, EtOH, or 1-PrOH.
• Co3O4 dispersions were similar, but clustering was found for water-impregnated catalysts.
• Higher FTS activities and selectivities were found for catalysts on untreated CNT.
• In situ XANES/XRPD indicated little difference in degree of reduction.

We report the preparation of supported cobalt catalysts (9 wt% Co) on untreated (CNT) and surface-oxidized (CNT-ox) carbon nanotube materials by incipient wetness impregnation with solutions of cobalt nitrate in water, ethanol, or 1-propanol. The results show that by a judicious selection of solvent and drying method, similar cobalt oxide particle sizes in the range of 4–5 nm on CNT and CNT-ox materials were obtained for the fresh catalysts. Cobalt particles supported on unfunctionalized CNT showed higher initial activities and C5+-selectivities than catalysts on functionalized CNT; however, the former catalysts were more prone to cobalt particle growth due to the lack of anchoring sites. The activities and cobalt particle sizes of catalysts after 60 h on stream revealed for particles larger than 6 nm a turnover frequencies (TOF) of 0.07 s−1 for Co/CNT and 0.03 s−1 for Co/CNT-ox. In situ XAS/XRPD studies showed a similar degree of reduction for the catalysts on untreated and oxidized CNT and the formation of hcp cobalt metal on untreated CNT which rationalizes the higher activity and TOF of the Co/CNT catalysts.

Figure optionsDownload high-quality image (120 K)Download as PowerPoint slide