Iron Carbides and Sodium-Sulphur Promotion in Fischer-Tropsch Synthesis Catalysts

Abstract

Currently, hydrocarbons are used in the vast majority of modern industrial processes leading to the production of transportation fuels, plastics, coatings and other materials. In the foreseeable future the current primary source for these hydrocarbons, namely crude oil from Earth’s crust, will be depleted and new alternatives as a source for hydrocarbons will be required. The industrial Fischer-Tropsch Process (FTP) is capable of converting a carbon-containing feedstock, such as natural gas, coal, biomass or municipal waste, into a variety of product hydrocarbons. The heterogeneously catalyzed Fischer-Tropsch Synthesis (FTS) reaction is employed in the FTP for converting a mixture of carbon monoxide (CO) and hydrogen (H2), better known as synthesis gas or syngas, into synthetic crude, which is further refined to the hydrocarbon products. In this PhD Dissertation, we have studied the FTS reaction using iron (Fe)-based, sodium (Na)-sulphur (S) promoted or unpromoted supported Fe(-Na-S)/α-Al2O3 catalyst materials. The main focus of this Dissertation has been on the characterization of the active phases of the catalyst materials catalyzing the FTS reaction, namely the in-depth characterization of Fe carbides. X-ray Diffraction (XRD) was applied as the primary characterization technique and the collected data were quantified with Rietveld Quantitative Phase Analysis (R-QPA). Fe carbide identification, formation conditions and their subtypes, as defined by carbide’s lattice parameters, were investigated. This PhD Dissertation defines the effects that the promotion of Na and S has on the Fe carbide formation and the carbides properties in the FTS reaction.