Fischer-Tropsch activity

Schulz, H., Claeys, M., and Harms, S. 1997. Effect of water partial pressure on steady state Fischer-Tropsch activity and selectivity of a promoted cobalt catalyst. Stud. Surf. Sci. Catal. 107 193-200. 

It can be concluded that CpCo(C0)2 does not possess Fischer-Tropsch activity, in accordance with the suggestions of others (10). 

The actual structure of the active catalyst in the above reactions is a matter of speculation. The evidence, however, points to the presence of a homogeneous but immobilized Fischer-Tropsch catalyst. Since soluble CpCo(CO)2 does not possess Fischer-Tropsch activity, this activity is a unique feature of the polymer-bound system. The finding that 5 is regenerated quantitatively upon exposure of the active Fischer-Tropsch catalyst resin to CO implies that the n5-cyclopentadienylcobalt bond remains intact throughout the Fischer-Tropsch reaction. Similar... 

The Fischer-Tropsch activity of resin 5 and the unique reaction conditions have important consequences. The use of a reaction solvent raises the possibility of controlling heat removal in this appreciably exothermic process. The apparent homogeneous nature of the catalytic species suggests that other soluble Fischer-Tropsch catalysts may be forthcoming. Finally, CpCo-(00)2 possesses catalytic activity not found in soluble CpCo-(00)2 this demonstrates that attachment to a polymer support not only may induce changes in catalytic activity of a transition metal complex, but also might give rise to completely new activity (51,52,53). 

Seemingly in contradiction to these results, it was reported that Fischer-Tropsch activity and selectivity are independent of particle size... 

It is well established that iron, cobalt and nickel supported catalysts may be used to convert CO and H2 to hydrocarbons by a process known as the Fischer-Tropsch synthesis. The problems of elucidation of mechanism and identification of active metal species have usually been tackled separately. Despite extensive research, neither aspect is well understood. In this paper Fischer-Tropsch activity is assessed in terms of the nature of the cobalt species present as part of the catalysts. 

Only the catalysts which exhibited Fischer-Tropsch activity consumed CO in TPC runs. This suggests that carbiding and FT polymerisation proceed via a conmon intermediate formed by dissociative CO chemisorption. All active FT catalysts examined promoted dissociative CO chemisorption below 200°C but none of these catalysts showed FT activity below 250°C. This is consistent with a CHx stepwise polymerisation being the rate determining step, as advocated by many workers (ref. 9). 

It has been shown that the dispersion of cobalt on various supports varies with the surface area and nature of the support. In the as-prepared calcined state the cobalt exhibits three reduction phases. Characteristics of the catalysts have been used to explain their Fischer-Tropsch activity. 

Fig. 21. Fischer-Tropsch activity of LaRhO) at different temperatures, as Schulz-Flory plots. (Reprinted by permission from Ref. 41.)...

Fischer-Tropsch activity, selectivity and deactivation data obtained in fixed bed reaction tests of Co/Si02 catalysts are summarized in Table 1. The turnover frequencies (TOFs) or site time yields based on H2 uptake and on rate measured after 20 hours of reaction agree within a factor of two with those reported for other cobalt catalysts [2, 3, 25-27]. CO conversion and methane selectivity versus time for Cab-O-Sil supported cobalt at both low and high space velocities are shown in Figure 1. It can be seen that at high conversion the catalyst deactivates rapidly while at low conversion the catalyst appears to be stable. The conversion is proportional to the water partial pressure thus water could be causing this deactivation. 

Syngas conversion offers a potential alternative to flaring or reinjection for monetization of associated gas. The Chevron s Gas Conversion Catalysis (GCC ) technology, a commercially viable hybrid syngas conversion catalyst comprising both a Fischer-Tropsch active metal and a zeolite component that provides the proper product distribution in favor of liquid hydrocarbons without the need for downstream hydroprocessing at high pressures is described in [99]. 

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