Reactions and Mechanisms of Fischer-Tropsch Synthesis

Fischer-Tropsch synthesis can be regarded as a surface polymerization reaction since monomer units are produced from the reagents hydrogen and carbon monoxide in situ on the surface of the catalyst (usually based on iron or cobalt). Hence, various hydrocarbons (mainly n-paraffins) are formed by successive addition of Ci units to growing chains on the catalyst surface. The main reaction of Fischer-Tropsch synthesis is therefore represented by  

The third reaction that plays an important role - above all if iron-based catalysts are used - is the unwanted formation of carbon dioxide by the water-gas shift reaction  

Since the discovery of the synthesis at the Kaiser Wilhelm Institute (Germany) in 1923 by Franz Fischer and Hans Tropsch, the kinetics of the Fischer-Tropsch synthesis have been studied extensively and many attempts have been made to describe the rate of reaction, either by using power law rate equations or equations based on certain mechanistic assumptions. In most cases, the rate of H2 and CO consumption is correlated with the (measurable) gas phase concentrations or partial pressures of H2, CO, and/or H2O. An overview of rate equations for iron catalysts is given by Huff and Satterfield (1984a) and for cobalt catalysts by Yates and Satterfield (1991). Details on the kinetics and reaction mechanism are, for example, discussed by Donnelly and Satterfield (1989), Dry (1982), Fernandes (2005), Huff and Satterfield (1984b), Post et al. (1989), Riedel et al. (1999), Schulz and Claeys (1999), Schulz et al. (1999), Van Steen and Schulz (1999), and Van Steen (1993). 

Termination, desorption (reduction by surface hydride giving an aikane or by hydride elimination giving an olefin) 

The probability of chain growth of a species with carbon number n is defined 

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