α-alumina as catalyst support in Co Fischer-Tropsch synthesis and the effect of added water; encompassing transient effects

Improving thermal diffusivity of supported Fe-based Fischer–Tropsch catalysts to enhance long-chain hydrocarbon production

Fischer Tropsch synthesis (FTS) is highly exothermic so heat removal remains crucial. In this study, a rational procedure is examined to remove heat in the FTS by improving the thermal diffusivity on a series of Fe-based catalysts.

The influence of hydrophobicity on Fischer-Tropsch synthesis catalysts

We review scientific works carried out on the influence of surface hydrophobicity on activity and product selectivity of supported cobalt and iron catalysts during Fischer-Tropsch synthesis (FTS). The characteristics of the surface of catalyst support may influence metal-support interactions, which leads to various degrees of metal dispersion and reducibility. Also, these support surface properties may influence the mass transfer of reactants and products at the catalyst active sites and subsequently affects the performance of the catalyst during FTS. Pre-silylated and post-silylated catalysts have been used to study the influence of surface hydrophobicity on the performance of FTS catalysts. The enhancement of FTS activity by hydrophobicity was mainly ascribed to the improved reducibility of metal oxide species. Furthermore, post-silylated supported iron catalysts favoured the suppression of water-gas shift (WGS) reaction, thereby hindering CO2 formation.

Significance of C3 Olefin to Paraffin Ratio in Cobalt Fischer–Tropsch Synthesis

The ratio between propene and propane (C3 o/p) during Fischer–Tropsch synthesis (FTS) has been analyzed based on both literature reports and experiments for five catalysts. The latter comprise four cobalt catalysts on γ-alumina with variations in pore sizes, and one catalyst on α-alumina. Overall variations include H2/CO feed ratio, residence time, water addition, transients between test conditions, CO conversion, cobalt particle size, promoter (Re), and support material. It was possible to rationalize all data based on secondary hydrogenation of olefins. In fact, it was deduced that olefins are dominating termination products in FTS, estimated to ca. 90% for C3, but that some paraffins most likely are also produced directly. Increased residence time and high H2/CO feed ratio favors olefin hydrogenation, while added water presumably displaces hydrogen on cobalt giving enhanced C3 o/p. High cobalt dispersion favors hydrogenation, as also promoted by Re. Effect of intraparticle diffusion is seen in transient periods; for example, as water is added or depleted. There is frequently positive correlation between C3 o/p and selectivity to longer chains; the latter expressed as C5+ selectivity, as both are sensitive to hydrogen activity. Some modifications, however, are needed due to the accepted volcano plot for C5+ selectivity with cobalt crystallite size. Titania as support shows unexpectedly low C3 o/p; probably due to SMSI (strong-metal-support-interaction).

Effect of Co-Feeding Inorganic and Organic Molecules in the Fe and Co Catalyzed Fischer–Tropsch Synthesis: A Review

This short review makes it clear that after 90 years, the Fischer–Tropsch synthesis (FTS) process is still not well understood. While it is agreed that it is primarily a polymerization process, giving rise to a distribution of mainly olefins and paraffins; the mechanism by which this occurs on catalysts is still a subject of much debate. Many of the FT features, such as deactivation, product distributions, kinetics and mechanism, and equilibrium aspects of the FT processes are still subjects of controversy, regardless of the progress that has been made so far. The effect of molecules co-feeding in FTS on these features is the main focus of this study. This review looks at some of these areas and tries to throw some light on aspects of FTS since the inception of the idea to date with emphasis and recommendation made based on nitrogen, water, ammonia, and olefins co-feeding case studies.