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

Abstract

The effect of a hydrogen pre-treatment step on an iron based Fischer–Tropsch catalyst applied to the CO hydrogenation reaction at 623 and 723K has been investigated by inelastic neutron scattering (INS). The catalyst cannot support methane production over a 6h period of reaction at 623K but it is active at 723K. The INS spectrum indicates the presence of a predominantly aliphatic hydrocarbonaceous overlayer for the post-reaction 623K sample, whereas the spectrum for the 723K 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.