A principal output from that body of work on FTS related surface chemistry is the realisation that, in addition to contributions from iron oxides, iron carbides, iron, amorphous carbon and graphite, the active phase of the FTS catalyst matrix is additionally comprised of a hydrocarbonaceous overlayer. An advantage of INS applied in this way is that the process of carbon laydown, commonly encountered with heterogeneous catalysts, does not interfere with spectral acquisition, as can often be the case with optical spectroscopic techniques such as infrared spectroscopy. The application of INS is beneficial, as it provides a means of obtaining the vibrational spectrum (50–4000 cm −1 in favourable circumstances) of the catalyst after a range of process operations. Ī body of work from the authors has used the technique of inelastic neutron scattering (INS) to investigate a range of iron-based FTS catalysts, with particular attention being paid to the catalyst conditioning phase. The topic of FTO catalysis has recently been reviewed by Wyckenhusen and Partall. Moreover, this combination of additives may additionally reduce methane yields. sodium or potassium) with a relatively small concentration of sulfur as chemical promoters is reported to enhance the selectivity to high value C 2–C 4 olefins. Namely, starting from a hematite foundation usually associated with classic FTS chemistry, the inclusion of a Group I cation (e.g. Although FTO catalysis is a relatively new field, there is an approaching consensus of what constitutes a viable FTO catalyst. Given that low molecular weight olefins constitute the chemical building blocks for the chemical manufacturing industry, there is an increasing interest in FTO chemistry. Here, modified iron-based catalysts are employed that switch the product slate away from long chain saturated hydrocarbons towards short chain olefins. The topic of FTS chemistry has been comprehensively reviewed by Van de Loosdrecht et al.Ī distinct variant of FTS that has recently come to the fore is the Fischer-Tropsch-to-olefins (FTO) process. The FTS process is heterogeneously catalysed, with iron or cobalt based catalysts finding wide application in numerous large-scale FTS operations located throughout the world. Subsequent hydro-treating of the complex product slate provides access to a range of useful hydrocarbons, for example sulfur-free diesel or aviation fuel. 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.įischer-Tropsch synthesis (FTS) is a well-established process for the conversion of carbon sources (coal, gas or biomass) into relatively large molecular weight saturated hydrocarbons.
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Specifically, whilst the sp 3 hybridised C–H modes of the hydrocarbonaceous overlayer are almost unaffected by the additives, the formation of the overlayer’s sp 2 hybridised C–H modes are noticeably impeded. Ex-situ inelastic neutron scattering measurements show the promoters perturb the formation of a previously described hydrocarbonaceous overlayer.
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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. 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).