The application of inelastic neutron scattering to investigate a hydrogen pre-treatment stage of an iron Fischer–Tropsch catalyst

• A hydrocarbonaceous overlayer is modified by a hydrogen pre-treatment step.
• The overlayer comprises partially hydrogenated polyaromatic hydrocarbons.
• The hydrogen pre-treatment stage is detrimental to CO hydrogenation activity.

The effect of a hydrogen pre-treatment step on an iron based Fischer–Tropsch catalyst applied to the CO hydrogenation reaction at 623 and 723 K has been investigated by inelastic neutron scattering (INS). The catalyst cannot support methane production over a 6 h period of reaction at 623 K but it is active at 723 K. The INS spectrum indicates the presence of a predominantly aliphatic hydrocarbonaceous overlayer for the post-reaction 623 K sample, whereas the spectrum for the 723 K sample is assigned to an overlayer comprising partially hydrogenated polycyclic aromatic compounds. The hydrocarbonaceous overlayer associated with the active phase of the catalyst is modified by the hydrogen pre-treatment step. The INS spectra are interpreted with reference to microreactor studies, powder X-ray diffraction, temperature-programmed oxidation and transmission electron microscopy. The hydrogen pre-treatment stage favours the formation of amorphous carbon and is deemed not to convey any advantage with respect to CO hydrogenation activity.

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