Fischer-Tropsch synthesis carbon monoxide effects

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. Hence, a variety of hydrocarbons (mainly n-paraffines) are formed from hydrogen and carbon monoxide by successive addition of C, units to hydrocarbon chains on the catalyst surface (Equation 12.1). Additionally, carbon dioxide (Equation 12.3) and steam (Equations 12.1 and 12.2) are produced C02 affects the reaction just a little, whereas H20 shows a strong inhibiting effect on the reaction rate when iron catalysts are used. 

According to the International Union of Pure and Applied Chemistry (IUPAC O)) the turnover frequency of a catalytic reac tion is defined as the number of molecules reacting per active site in unit time. The term active sites is applied to those sites for adsorption which are effective sites for a particular heterogeneous catalytic reaction. Because it is often impossible to measure the amount of active sites, some indirect method is needed to express the rate data in terms of turnover frequencies In some cases a realistic measure of the number of active sites may be the number of molecules of some compound that can be adsorbed on the catalyst. This measure is frequently used in the literature of the Fischer-Tropsch synthesis, where the amount of adsorption sites is determined by carbon monoxide adsorption on the reduced catalyst. However, it is questionable whether the number of adsorption sites on the reduced catalyst is really an indication of the number of sites on the catalyst active during the synthesis, because the metallic phase of the Fischer-Tropsch catalysts is often carbided or oxidized during the process. 

The variation in promoter ability of (i) potassium and rubidium carbonates and (ii) the other carbonates may be attributable to subtle effects the active carbonates have on the surfaces and active sites of the catalyst. These effects may be caused by differences in basicity of the carbonates. According to Dry et al. (23), the promoter which is the strongest base is the most effective. The influence of base promoters on Fischer-Tropsch synthesis depends on their effect on the heat of adsorption of carbon monoxide and hydrogen on the catalyst, e.g., K2O increases the heat of carbon monoxide adsorption at low coverage and decreases the initial heat of hydrogen adsorption. 

Fischer-Tropsch synthesis (FTS), directly converting a mixture of carbon monoxide and hydrogen (syngas) into sulfur-free hydrocarbons, has attracted much attention from academic and industrial community. However, the development of FTS mainly depends on experience, resulting in the inefficient development of catalysts and industrialization design. Recently, a new analysis method, mesoscale analysis, has attracted more attention due to researching on between different scales or crossing several scales, which would contribute to efficient R D process of FTS. This chapter will summarize the multiscale effects on FTS products distribution such as ASF distribution, kinetic model. 

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