Carbon deposition on Co catalysts during Fischer–Tropsch synthesis: A computational and experimental study

The deactivation of a 20 wt% Co/γ-Al2O3 catalyst during Fischer–Tropsch Synthesis (FTS) at 240 °C, 20 bar, and a H2:CO ratio of 2 was studied in a fixed-bed micro-reactor. The CO conversion had reduced by 30% after 200 h, and both carbidic and polyaromatic carbon species could be detected on the catalyst using a combination of Temperature-Programmed Hydrogenation (TPH), X-ray Photoelectron Spectroscopy (XPS) and High Resolution Transmission Electron Microscopy (HRTEM). Using Density Functional Theory (DFT), the relative stability of different types of deposited carbon on the Co catalyst was evaluated. Extended layers of graphene were the most stable form, followed by a p4g surface carbide phase initiating from the step edges. Both are more stable than surface CH2 groups by 99 and 79 kJ/mol. The calculated C 1s core-level binding energies of 284.5 and 283.4 eV further support the presence of polyaromatic carbon and of a surface carbide.