Co-based Fischer-Tropsch Catalysts

We now discuss the main literature results on Mn-promotion for unsupported as well as supported Fe-, Ru-, and Co-based Fischer-Tropsch catalysts. Such comparison between Fe-, Ru- and Co-based catalysts has been shown to be very useful because it places the role of Mn as a promoter in F-T catalysis in a broader perspective. 

Rygh, L.E.S., and Nielsen, C.J. 2000. Infrared study of CO adsorbed on a Co/Re/-Al203-based Fischer-Tropsch catalyst. J. Catal. 194 401-9. 

At this point, the system was tested with catalyst for activation and FTS, in the hopes that the seal leak rates would be impeded by the presence of small catalyst particles. The FTFE 20-B catalyst (L-3950) (Fe, 50.2% Cu, 4.2% K, 1.5% and Si, 2.4%) was utilized. This is part of the batch used for LaPorte FTS run II.20 The catalyst was activated at 543 K with CO at a space velocity (SV) of 9 sl/h/g catalyst for 48 h. A total of 1,100 g of catalyst was taken and 7.9 L of C30 oil was used as the start-up solvent. At the end of the activation period, an attempt was made for Fischer-Tropsch synthesis at 503 K, 175 psig, syngas SV = 9 sl/h/g catalyst, and H2/CO = 0.7. However, the catalyst was found to be completely inactive for Fischer-Tropsch synthesis. Potential reasons for catalyst poisoning under present experimental conditions were investigated. Sulfur and fluorine are known to poison iron-based Fischer-Tropsch catalysts.21,22 Since the stator of the pump is... 

In many respects the SMDS process (Figure 18.8) precipitated a change in the Fischer-Tropsch community with respect to the preferred catalyst for Fischer-Tropsch synthesis and the approach to product workup. It is therefore instructive to understand why Shell moved away from iron-based Fischer-Tropsch catalysts (and as a consequence also high-temperature synthesis) and opted for a Co-LTFT process with an uncomplicated refinery design that does not produce... 

Since cobalt on kieselguhr in one of the original Fischer-Tropsch catalysts (1-9), it appeared attractive to investigate the catalytic activity of cobalt complexes immobilized on polystyrene. Although there are many supported cobalt-based Fischer-Tropsch catalysts known (see, for example, references 18-21), no polystyrene-bound systems had been reported. During the course of our work 18% (22,60,61) and 20% (23) crosslinked analogs of CpCo(C0)2 were shown to exhibit limited catalytic activity but no CO reduction. A preliminary disclosure of our work has appeared (2)4). 

Mn-promoted Fe-based Fischer-Tropsch Catalysts. 4.1.1 Unsupported Fe-Mn Fischer-Tropsch Catalysts. Iron-based F-T catalysts possess both hydrogenation and WGS activity, imposing a flexible option as a working catalyst for typically coal-derived CO-rich syngas conversion. Iron-based catalysts often contain small amounts of K and some other metals/metal oxides as promoters to improve their activity and selectivity. Mn has been widely used as one of the promoters for unsuppported Fe-based F T catalysts, particularly in promoting the production of C2 C4 olefins. ... 

The characterization tools to investigate cobalt-based Fischer-Tropsch catalysts are mostly used to study the catalyst materials under conditions far from industrially relevant reaction conditions i.e., in the presence of CO and H2, as well as of the reaction products, including H2O at reaction temperatures and at high pressures. Since catalytic solids are dynamic materials undergoing major changes under reaction conditions it can be anticipated that the currently obtained information on the active site is at least incomplete. This holds also for the active state and location of the promoter element under reaction conditions. For example, an electronic elfect on the cobalt active phase induced by a promoter element can maybe exist only at high pressures and will remain -due to the lack of the appropriate instrumentation - unnoticed to the catalyst... 

Iron-based Fischer-Tropsch synthesis (FTS) catalysts are preferred for synthesis gas with a low H2/CO ratio (e.g., 0.7) because of their excellent activity for the water-gas shift reaction, lower cost, lower methane selectivity, high olefin... 

LEIS has been applied to study the surface composition of Co-Mo and Ni-Mo hydrodesulfurization catalysts [46-48], Fe-based Fischer-Tropsch [49] and ammonia synthesis catalysts [50], and model systems such as Pt evaporated on Ti02 [51]. The review of Horrell and Cocke [52] describes several applications. 

Fischer-Tropsch Catalysts. - It is well known that all Group VIII transition metals are active for F-T synthesis. However, the only F-T catalysts, which have sufficient CO hydrogenation activity for commercial application, are composed of Ni, Co, Fe or Ru as the active metal phase. These metals are orders-of-magnitude more active than the other Group VIII metals and some characteristics of Ni-, Fe-, Co- and Ru-based F-T catalysts are summarized in Table 2. 

Very recently Geus and co-workers [44, 45] have applied another method based on chemical complexes. This is the complex cyanide method to prepare both monocomponent (Fe or Co) and multicomponent Fischer-Tropsch catalysts. A large range of insoluble complex cyanides are known in which many metals can be combined, e.g. iron(n) hexacyanide and iron(m) hexacyanide can be combined with iron ions, but also with nickel, cobalt, copper, and zinc ions. Soluble complex ions of molybdenum(iv) which can produce insoluble complexes with metal cations are also known. Deposition precipitation (Section A.2.2.1.5) can be performed by injection of a solution of a soluble cyanide complex of one of the desired metals into a suspension of a suitable support in a solution of a simple salt of the other desired metal. By adjusting the cation composition of the simple salt solution, with a same cyanide, it is possible to adjust the composition of the precursor from a monometallic oxide (the case when the metallic cation is identical to that contained in the complex) to oxides containing one or several foreign elements. 

Iron-based Fischer-Tropsch (FT) catalysts undergo a series of phase transformations during activation and use (1). Activation with carbon monoxide or syngas typically results in the conversion of Fe O to Fe O and ultimately to one or more iron carbides (2). During FT synthesis, iron carbides can be oxidized to Fe O if the or COj/CO ratios are high... 

Ternary composites have also been used comprising a Fischer-Tropsch catalyst, a methanol synthesis catalyst, and a zeolite [100]. Two Fe-based catalysts (ie, one promoted by K and the other by Ru), two HY zeolites with different acidities, a commercial HZSM-5, and Cu/ZnO/AljOj (methanol synthesis catalyst) were tested in these composites. Dimethyl ether (DME), methanol, and hydrocarbons were formed. Addition of the Cu/ZnO/Al Oj catalyst to a binary mixture of a Fischer-Tropsch catalyst and HZSM-5 results in the increase of the CO conversion by more than 20 times. The DME selectivity decreases as the conversion increases. Y zeolites and the Fischer-Tropsch synthesis catalyst promoted by Ru generated the most active composites. The role of zeolites in the ternary composite is assumed with the DME synthesis. First, methanol is synthesized from syngas on Cu/ZnO/Al Oj then it is dehydrated by an acid catalyst to produce DME and finally, DME initiates FT synthesis, which is then propagated by CO. 

Sasol Fischer-Tropsch Process. 1-Propanol is one of the products from Sasol s Fischer-Tropsch process (7). Coal (qv) is gasified ia Lurgi reactors to produce synthesis gas (H2/CO). After separation from gas Hquids and purification, the synthesis gas is fed iato the Sasol Synthol plant where it is entrained with a powdered iron-based catalyst within the fluid-bed reactors. The exothermic Fischer-Tropsch reaction produces a mixture of hydrocarbons (qv) and oxygenates. The condensation products from the process consist of hydrocarbon Hquids and an aqueous stream that contains a mixture of ketones (qv) and alcohols. The ketones and alcohols are recovered and most of the alcohols are used for the blending of high octane gasoline. Some of the alcohol streams are further purified by distillation to yield pure 1-propanol and ethanol ia a multiunit plant, which has a total capacity of 25,000-30,000 t/yr (see Coal conversion processes, gasification). 

Jacobs, G., Das, T.K., Li, J., Luo, M., Patterson, P.M., and B.H. Davis. 2007. Fischer-Tropsch synthesis Influence of support on the impact of co-fed water for cobalt-based catalysts. In Fischer-Tropsch synthesis Catalysts and catalysis, ed. B.H. Davis and M.L. Occelli, 217-53 Amsterdam, The Netherlands Elsevier. 

---