Hydrocarbons Fischer-Tropsch catalyst

Synthetic Fuels. Hydrocarbon Hquids made from nonpetroleum sources can be used in steam crackers to produce olefins. Fischer-Tropsch Hquids, oil-shale Hquids, and coal-Hquefaction products are examples (61) (see Fuels, synthetic). Work using Fischer-Tropsch catalysts indicates that olefins can be made directly from synthesis gas—carbon monoxide and hydrogen (62,63). Shape-selective molecular sieves (qv) also are being evaluated (64). 

The production of hydrocarbons using traditional Fischer-Tropsch catalysts is governed by chain growth or polymerization kinetics. The equation describing the production of hydrocarbons, commonly referred to as the Anderson-Schulz-Flory equation, is ... 

Hydrocarbons over a Cobalt-Thoric Fischer-Tropsch Catalyst. J. Amer. chem. Soc. 73, 5213 (1951)-... 

Khodakov A.Y., Chu W., and Fongarland P. 2007. Advances in the development of novel cobalt Fischer-Tropsch catalysts for synthesis of long-chain hydrocarbons and clean fuels. Chem. Rev. 107 1692-744. 

Weller, S. E. 1947. Kinetics of carbiding and hydrocarbon synthesis with cobalt Fischer-Tropsch catalysts. J. Am. Chem. Soc. 69 2432-36. 

Roberts, G. W., and Kilpatrick, P. K. 2001. Methods and apparatus for separating Fischer-Tropsch catalysts from liquid hydrocarbon product. U.S. Patent 6217830. 

Finding ethane to be the major product is a significant result, because for all the other systems described above, and indeed for Fischer-Tropsch catalysts in general, methane is the major hydrocarbon product. Furthermore, as is discussed in Section III, high selectivity to C2 could have important mechanistic as well as commercial implications. 

A Fischer-Tropsch catalyst system capable of linking reactions (14) and (16), i.e., a synthesis catalyst having appreciable shift activity, would clearly be of considerable interest in that it would allow the use of hydrogen-poor synthesis gas for the production of hydrocarbons via the following overall reaction ... 

The data available for heterogeneous Fischer-Tropsch catalysts indicate that with cobalt-based catalysts the rate of the water gas-shift reaction is very slow under the synthesis conditions (5). Thus, water is formed together with the hydrocarbon products [Eq. (14)]. The iron-based catalysts show some shift activity, but even with these catalysts, considerable quantities of water are produced. 

There has been considerable recent research interest in the activation of carbon monoxide en route to more complex organic molecules. Among the various reactions that have been investigated and/or newly discovered, the transition metal catalyzed reduction of CO to hydrocarbons (Fischer-Tropsch synthesis) has enjoyed particular attention (l- ). Whereas most of the successful efforts in this area have been directed toward the development of heterogeneous catalysts, there are relatively few homogeneous systems. Among these, two are based on clusters (10,11) and others are stoichiometric in metal (12-17). In this report we detail the synthesis and catalytic chemistry of polystyrene ( ) supported... 

The incorporation of a ZSM-5 class zeolite into a ruthenium Fischer-Tropsch catalyst promotes aromatics formation and reduces the molecular weight of the hydrocarbons produced. These composite catalysts can produce a high octane aromatic gasoline in good yield in a single step directly from synthesis gas. 

In the very active field of unmodified nanoparticles recent discoveries have been made on size-selective Fischer-Tropsch catalysts that convert selectively CO and H2 into hydrocarbons there is a strong dependence of activity, selectivity and Hfetime on Co particle size. This topic of unmodified, supported or unsupported, nanoparticles is outside the scope of this chapter [74, 75]. Nevertheless, we mention discoveries made by Degussa, who have patented a process for H2O2 synthesis from molecular oxygen and molecular hydrogen with nanosized Pd particles (6 A) [76]. 

Supported Co-Mn Fischer-Tropsch Catalysts. F-T synthesis of lower hydrocarbons on silicalite-1 supported Co and Co-Mn catalysts was reported by Das et C03O4 was found to be the only phase present in Mn-free... 

Mechanism of Hydrocarbon Synthesis over Fischer Tropsch Catalysts P. Biloen and W. M. H. Sachtler Surface Reactions and Selectivity in Electro-catalysis... 

These new data acquired with double-labeled vinyl probes (13CH2=13CHBr and 13CH2=13CH2) determined first on Rh, but found to be similar for more common Fischer-Tropsch catalysts (Ru, Fe, Co) showed that these are readily incorporated into the alkene and the alkane products. In addition, an increase in the rate of hydrocarbon formation was observed during vinylic but not ethyl addition. These data indicate that the participation of vinyl intermediates is an integral part of the surface polymerization mechanism, specifically, vinyl (alkenyl) intermediates couple with surface methylene in hydrocarbon formation ... 

Dautzenberg et al. (3) have determined the kinetics of the Fischer-Tropsch synthesis with ruthenium catalysts. The authors showed, that because the synthesis can be described by a consecutive mechanism, the non steady state behaviour of the catalyst can give information about the kinetics of the process. On ruthenium they found that not only the overall rate of hydrocarbon production per active site is small, but also that the rate constant of propagation is low. Hence, Dautzenberg et al. find that the low activity of Fischer-Tropsch catalysts is due to the low intrinsic activity of their sites. On the other hand, Rautavuoma (4) states that the low activity of cobalt catalysts is due to a small amount of active sites, the amount being much smaller than the number of adsorption sites measured. 

Biloen P, Sachtler WMH. Mechanism of hydrocarbon synthesis over Fischer-Tropsch catalysts. Adv Catal. 1981 30 165-216. 

FIGURE 5 Anderson-Schulz-Flory distribution of the linear hydrocarbons, linear oxygenates (n-alcohols, n-aldehydes, and linear carboxylic acids), and methyl alkyl ketones formed in the Fischer-Tropsch synthesis on an iron-containing Fischer-Tropsch catalyst operating at a temperature of 498 K (plotted using log(lO)). 

These trends are consistent with observations made to characterize the chain growth of surface carbon that was deposited by methane decomposition. In a row of the periodic table, the selectivity to hydrocarbon formation was foimd to increase from right to left for example, palladium shows a lower selectivity than ruthenium 111,112). Metals such as platinum and iridium are characterized by higher selectivities for chain growth initiated from "Cl" species than other metals because of their relatively high M—C bond energies. However, platinum and iridium are unsuitable as Fischer-Tropsch catalysts because the dissociation of CO is too slow. 

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