Fischer-Tropsch (FT) chemistry allows access to a wide range of hydrocarbon products via catalytic polymerisation of synthesis gas (syngas) over an iron or cobalt catalyst. The resulting hydrocarbon products have a variety of applications, from chemical industry feedstocks to producing high purity diesel. The actual active phase/ species responsible for activity in iron based FT catalyst is still an issue of debate. One of the reasons for the disparity of opinion is the variety of species that form during the process. Furthermore, as carbon is deposited on the surface of the catalyst, analysis using conventional surface spectroscopic methods such as infrared becomes increasingly difficult. Inelastic neutron scattering (INS) has been utilised due to its ability to characterise hydrogen-containing species and to overcome the constraints discussed previously with infrared. Due to the anomalously high neutron cross section of 1H, INS provides the means of detecting the vibrational modes of hydrogeneous species over a wide spectral range (20-4000 cm-1) and at reasonable resolution.In this study, INS has been applied to probe an industrially reacted Fe FT catalyst. The recovered sample has undergone an extraction procedure to remove the conventional hydrocarbon residue products associated with industrial FT chemistry. Therefore any hydrocarbonaceous features present in the INS spectrum are component of the catalyst rather than a product of the FT reaction. In addition a laboratory prepared Fe-based FT catalyst has been tested for CO hydrogenation at ambient pressure and investigated by INS. Although CO hydrogenation is not formally regarded as FT chemistry as no polymerisation reaction takes place, it does address aspects of Fe/CO/H2 surface chemistry that must have some connectivity to the molecular transformations associated with FTS. Furthermore the formation of CH4 by CO hydrogenation avoids formation of long chain or heavy hydrocarbon products, simplifying INS analysis.

Application of inelastic neutron scattering to probe iron based Fischer-Tropsch catalysts

247th National Meeting (2014)

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