Fischer-Tropsch reaction Subject

The mechanism of the Fischer-Tropsch reactions has been the object of much study (note Eqs. XVI11-55-XV111-57) and the subject of much controversy. Fischer and Tropsch proposed one whose essential feature was that of a metal carbide—patents have been issued on this basis. It is currently believed that a particular form of active adsorbed carbon atoms is involved, which is then methanated through a series of steps such as... 

Even if hydrides of transition metals play an important role as intermediates in catalytic processes such as hydrogenation and hydro-formylation of alkenes and the Fischer-Tropsch reaction,71 in order to follow with the bioinorganic subject, we refer to the interconversion process ... 

While current applications include hydrogenation and fermentation, slurry bubble columns have recently been the subject of renewed study for use in two areas of hetergeneous catalysis, SRC coal liquefaction and the Fischer-Tropsch reaction to produce hydrocarbons from synthesis gas. 

The conversion of iron catalysts into iron carbide under Fischer-Tropsch conditions is well known and has been the subject of several studies [20-23], A fundamentally intriguing question is why the active iron Fischer-Tropsch catalyst consists of iron carbide, while cobalt, nickel and ruthenium are active as a metal. Figure 5.9 (left) shows how metallic iron particles convert to carbides in a mixture of CO and H2 at 515 K. After 0.5 and 1.1 h of reaction, the sharp six-line pattern of metallic iron is still clearly visible in addition to the complicated carbide spectra, but after 2.5 h the metallic iron has disappeared. At short reaction times, a rather broad spectral component appears - better visible in carburization experiments at lower temperatures - indicated as FexC. The eventually remaining pattern can be understood as the combination of two different carbides -Fe2.2C and %-Fe5C2. 

Cobalt-based Fischer-Tropsch catalysts are the subject of continuing interest as large-scale Gas-to-Liquids plants come on line. Fernando Morales and Bert Weckhuysen (Utrecht University, the Netherlands) look specifically at the effects of various promoters for these catalysts, particularly Mn. The effect of these promoters in controlling the activity and selectivity of the overall reaction can be critical in the overall process economics. This chapter also looks at new spectroscopic techniques that have recently been used to study the effects of these promoters. 

The ability of a p-carbene to react with an unsaturated hydrocarbon and form an enlarged dimetallocycle encourages speculation over their role in such processes as alkene metathesis and Fischer-Tropsch synthesis. In Scheme 6 a possible mechanism for metathesis initiated by a p-carbene is presented, owing much to other workers (T7,22). Reactions of p-carbenes with alkenes are under investigation in our laboratory. Recently Pettit has observed that the p-methylene complex [Fe2(C0)8(p-CH2)] generates propene when subjected to a pressure of ethene and has also suggested the intermediacy of a three-carbon dimetallocycle (23). 

Assuming that olefin intermediates are produced on the surface of the Fischer-Tropsch catalyst, similar mechanisms for chain growth have been suggested. Alcoholic intermediates also have been proposed based on the isotope-labeling studies of Emmett et al. on iron surfaces. The understanding and control of the insertion reaction appears to be the key for controlling the product distribution. Clearly the mechanism of this reaction will be subjected to close scrutiny in the near future. 

Hydrogenation of Carbon Monoxide or Carbon Dioxide. There are two important aspects of metal carbides in CO-H2 reactions including methana-tion, Fischer-Tropsch synthesis, alcohol synthesis, and water gas shift reaction. First, metal carbides, by themselves or together with other phases, are considered as active phases in these reactions catalyzed by Fe, Co, and Ni. These carbide phases are formed in situ from the respective metals or oxides during the reaction. This aspect is not discussed here. Instead, catalysis by early transition metals intentionally prepared in a stable carbide form is the subject of this section. Molybdenum and tungsten carbides are by far the most extensively studied. 

The basic reaction was discovered in 1923 by F. Fischer and H. Tropsch, working at the Kaiser Wilhelm Institute for Coal Research in Miilheim, Germany. In 1984, Mako and Samuel wrote, The quantity of patents and literature that has appeared on the subject in the past 60 years makes it virtually impossible to retrace stepwise the developments of the Fischer-Tropsch synthesis. The first full-scale plant was built by Ruhrchemie at Holten, from 1934 to 1936 by 1939, eight more plants had been built in Germany. All of these plants were disabled by air attacks in 1944. Used in the SASOL coal gasification plant in South Africa. The first modern Fischer-Tropsch plant outside Africa was built by Shell in Malaysia in 1993, based on natural gas. 

It is particularly important to gather a large number of search terms, which are closely related to the search topic when carrying out a literature search about a subject as extensive as the Fischer-Tropsch synthesis in order to ensure that even publications, which do not include the term Fischer-Tropsch synthesis, but report on research results of this reaction, are also found. In both manual and computer assisted searches compiling search terms is the most important step, as this is the development of a search profile. Once again the Index Guide is indispensable for this purpose, and every search, whether online or manual, should start with the Index Guide. 

The search for subject-oriented terms concerning the Fischer-Tropsch synthesis will be abandoned here. The Index Guide also contains a cross-reference to the Fischer-Tropsch synthesis which leads to the Chemical Substance Index, namely the entry carbon monoxide reactions, hydrogenation of (Fig. 44). The addition of reactions serves as a reminder that the abstracts about carbon monoxide are assigned to various subgroups by qualifiers and categories. 

The oldest information on the subject is in early patents of BASF on alkahzed Co catalysts, and the patents by Fischer and Tropsch on the so called synthol process. More recently, several papers by the Bureau of Mines Laboratory S have demonstrated that an interesting amount of oxygenates can be produced with standard alkali-promoted Fe catalysts, when proper reaction conditions are chosen and when the catalyst is properly run in . 

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