The application of inelastic neutron scattering to explore the significance of a magnetic transition in an iron based Fischer-Tropsch catalyst that is active for the hydrogenation of CO

Abstract

An iron based Fischer-Tropsch synthesis catalyst is evaluated using CO hydrogenation at ambient pressure as a test reaction and is characterised by a combination of inelastic neutron scattering (INS), powder X-ray diffraction, temperature-programmed oxidation, Raman scattering, and transmission electron microscopy. The INS spectrum of the as-prepared bulk iron oxide pre-catalyst (hematite, α-Fe2O3) is distinguished by a relatively intense band at 810 cm(-1), which has previously been tentatively assigned as a magnon (spinon) feature. An analysis of the neutron scattering intensity of this band as a function of momentum transfer unambiguously confirms this assignment. Post-reaction, the spinon feature disappears and the INS spectrum is characterised by the presence of a hydrocarbonaceous overlayer. A role for the application of INS in magnetic characterisation of iron based FTS catalysts is briefly considered.

Application of Inelastic Neutron Scattering to the Methanol-to-Gasoline Reaction Over a ZSM-5 Catalyst

“…This attribute is particularly accessible on direct geometry instruments such as MAPS and MERLIN [15,16]. A commonly adopted means of visualising this information is to use ''mitre'' plots [26], where the neutron scattering intensity is plotted as a function of energy (x, y axis) and momentum transfer (Q, x axis). Figure 2 shows the S(Q,x) mitre plots recorded on the MERLIN spectrometer for the clean (left hand frame) and reacted (right hand frame) samples with 4840 cm -1 incident energy.…”

“…That work also outlines an increasing trend of using of INS to examine a variety of heterogeneously catalysed reaction systems [15]. For example, following on from the work of Silverwood et al who used INS to examine alumina-supported nickel catalysts applied to the dry [18-21] and steam [22] reforming of methane, Warringham and co-workers have used a combination of indirect [23] and direct [24][25][26] geometry INS spectrometers to investigate iron based FischerTropsch synthesis (FTS) catalysts. Moreover, Warringham et al [27] recently reported on sample environment details relevant to the acquisition of INS spectra of heterogeneous catalysts.…”

The Application of Quasi-Elastic Neutron Scattering to Investigate Hydrogen Diffusion in an Iron-Based Fischer–Tropsch Synthesis Catalyst

“…The iron oxide catalyst sample used for this investigation was prepared using the co-precipitation of iron nitrate (Sigma Aldrich, 99.99%) and sodium carbonate (Sigma-Aldrich, 99.99%). The preparative procedure utilises a batch reactor apparatus for reproducible sample synthesis and is described elsewhere [14]. The resulting slurry is filtered and washed with warm deionised water followed by a calcination step involving a step wise heating programme, with a maximum temperature of 623 K [14].…”

“…The preparative procedure utilises a batch reactor apparatus for reproducible sample synthesis and is described elsewhere [14]. The resulting slurry is filtered and washed with warm deionised water followed by a calcination step involving a step wise heating programme, with a maximum temperature of 623 K [14]. The procedure produces hematite (α-Fe 2 O 3 ) and an absence of promoters/modifiers.…”

“…Previous work has utilised neutron spectroscopic techniques, in particular inelastic neutron scattering (INS) for the investigation of iron FTS systems, allowing for identification of hydrogenous moieties in post-reaction iron FTS catalysts [9,10]. Alongside complimentary analytical techniques such as XRD, Raman, temperature-programmed oxidation (TPO) and TEM, INS has been used to investigate both the evolutionary profile of the active phase of the catalyst as well as the development of a hydrocarbonaceous overlayer [8,[11][12][13][14]. These investigations have utilised a promoterfree iron-based catalyst (α-Fe 2 O 3 ) and have examined its evolutionary profile over a 24 h period using ambient pressure CO hydrogenation conditions as a representative FTS reaction [8].…”