An Inelastic Neutron Scattering Investigation of the Temporal Behaviour of the Hydrocarbonaceous Overlayer of a Prototype Fischer-Tropsch to Olefins Catalyst

Abstract

A dual sodium and sulfur promoted haematite, representative of a candidate Fischer-Tropsch to olefins (FTO) catalyst, is prepared and contrasted with the performance of an unpromoted hematite sample in the ambient pressure CO hydrogenation reaction at 623 K as a function of time-on-stream (0–24 h). In-situ post-reaction temperature-programmed oxidation measurements show the carbon evolutionary phase of the catalyst conditioning process to be retarded for the FTO catalyst. Ex-situ inelastic neutron scattering measurements show the promoters perturb the formation of a previously described hydrocarbonaceous overlayer. Specifically, whilst the sp3 hybridised C–H modes of the hydrocarbonaceous overlayer are almost unaffected by the additives, the formation of the overlayer’s sp2 hybridised C–H modes are noticeably impeded. The results are discussed in terms of the Na/S promoters disturbing the formation of an ordered hydrocarbonaceous overlayer that is thought to constrain the supply of adsorbed hydrogen atoms, which favours the formation of unsaturated hydrocarbons associated with the FTO process.

Net Zero and Catalysis: How Neutrons Can Help

“…Running the same reaction at 1 bar results in only methane formation, so all the products are gaseous, but the catalyst is the same in both cases. This model reaction has been used for extensive studies of iron-based catalysts for both FTS [49][50][51][52][53] and FTO [54][55][56].…”

“…The INS studies reported in [48][49][50][51][52][53][54][55][56] all concern iron-based catalysts and there is clearly more that could be done, particularly regarding the effect of the additives that direct FTS to FTO. The cobalt-based systems have not been investigated by neutron scattering, apart from a study that aimed to characterise the states of adsorbed hydrogen on a range of cobalt catalysts [57].…”