Iron catalysts reaction products

Davis, B. H. Miller. S. J. Slurry-phase Fischer-Tropsch reaction over potassium-promoted iron catalysts for production ofoleiln-rich diesel fuel and lubricating base oil feedstocks. US Patent 6602922. 2003. 

The tertiary metal phosphates are of the general formula MPO where M is B, Al, Ga, Fe, Mn, etc. The metal—oxygen bonds of these materials have considerable covalent character. The anhydrous salts are continuous three-dimensional networks analogous to the various polymorphic forms of siHca. Of limited commercial interest are the alurninum, boron, and iron phosphates. Boron phosphate [13308-51 -5] BPO, is produced by heating the reaction product of boric acid and phosphoric acid or by a dding H BO to H PO at room temperature, foUowed by crystallization from a solution containing >48% P205- Boron phosphate has limited use as a catalyst support, in ceramics, and in refractories. 

Fischer Tropsch synthesis is catalyzed by a variety of transition metals such as iron, nickel, and cobalt. Iron is the preferred catalyst due to its higher activity and lower cost. Nickel produces large amounts of methane, while cobalt has a lower reaction rate and lower selectivity than iron. By comparing cobalt and iron catalysts, it was found that cobalt promotes more middle-distillate products. In FTS, cobalt produces... 

A mechanistic proposal, which is based on the mthenium-catalyzed dehydration reaction reported by Nagashima and coworkers [146], is shown in Scheme 44. Reaction of a primary amine with hydrosilane in the presence of the iron catalyst affords the bis(silyl)amine a and 2 equiv. of H2. Subsequently, the isomerization of a gives the A,0-bis(silyl)imidate b and then elimination of the disiloxane from b produces the corresponding nitrile. Although the disiloxane and its monohydrolysis product were observed by and Si NMR spectroscopy and by GC-Mass-analysis, intermediates a and b were not detected. 

In addition, also nonheme iron catalysts containing BPMEN 1 and TPA 2 as ligands are known to activate hydrogen peroxide for the epoxidation of olefins (Scheme 1) [20-26]. More recently, especially Que and coworkers were able to improve the catalyst productivity to nearly quantitative conversion of the alkene by using an acetonitrile/acetic acid solution [27-29]. The carboxylic acid is required to increase the efficiency of the reaction and the epoxide/diol product ratio. The competitive dihydroxylation reaction suggested the participation of different active species in these oxidations (Scheme 2). 

It has been suggested [21,22] that the presence of Cu and K increases the rates and extent of Fe304 carburization during reaction and the FTS rates, by providing multiple nucleation sites that lead to the ultimate formation of smaller carbide crystallites with higher active surface area. In the present investigation, Cu- and K-promoted iron catalysts performed better than the unpromoted catalysts in terms of (1) a lower CH4 selectivity, (2) higher C5+ and alkene product selectivi-ties, and (3) an enhanced isomerization rate of 1-alkene. 

An example of activity developing with a Co catalyst is shown in Figure 9.9 (right). CO-conversion (respectively the yield of products) increases with time by a factor of about 10, from ca. 4% to ca. 55%.7,17 Figure 9.9 (left) shows the time dependence of FT with an iron catalyst. There are a strong initial carbon deposition (referring to iron carbide formation) and fast water gas shift reaction, and FT... 

One way to get a representative product distribution for a specific period is to remove all FT products in the reactor system and replace them with a substance that will not influence selectivity determination. The FT reaction is then run for a specific period, after which a full analysis can be done that will represent only the products produced during that specific period. In Figure 13.8, data are presented for a run started with the catalyst suspended in a highly paraffinic wax (FT HI wax, C30-C90). After a certain time of synthesis, the FT run was stopped and the catalyst placed under inert conditions (argon). The reactor content was then displaced with degassed and dried polyalphaolefin oil (Durasyn). After restarting the FT synthesis, the total product spectrum was determined (HI run after displacement). It was found that the value of a2 was much lower than before the displacement of the HI wax. In fact, the a2 values were quite comparable to those measured when the FT synthesis was started up with Durasyn (compare with Durasyn runs 1, 2, and 3). This clearly illustrates the impact that the reactor medium used to start the FT reaction can have on the determination of the a-value. The results further show that there was no change in the value of a2 of the iron catalyst up to 500 h on-line. 

Traditionally, iron-based catalysts have been used for FT synthesis when the syngas is coal derived, because of their activity in both FTS and WGS reactions. Complex mixtures of straight-chain paraffins, olefins, and oxygenate (in substantial proportions) compounds are known to be formed during iron-based FTS. Olefin selectivity of iron catalysts is typically greater than 50% of the hydrocarbon products at low carbon numbers, and more than 60% of the produced olefins are a-olefins.13 For iron-based catalysts, the olefin selectivity decreases asymptotically with increasing carbon number. 

Industrially, ammonia has been produced from dinitrogen and dihydrogen by the Haber-Bosch process, which operates at very high temperatures and pressures, and utilizes a promoted iron catalyst. Millions of tons of ammonia are generated annually for incorporation into agricultural fertilizers and other important commercial products. The overall reaction is exergonic, as indicated in equation 6.1 ... 

If the reaction in which the metallic fraction serves as a catalyst produces water as a by-product, it may well be that the catalyst converts back to an oxide. One should always be aware that in fundamental catalytic studies, where reactions are usually carried out under differential conditions (i.e. low conversions) the catalyst may be more reduced than is the case under industrial conditions. An example is the behavior of iron in the Fischer-Tropsch reaction, where the industrial iron catalyst at work contains substantial fractions of Fe304, while fundamental studies report that iron is entirely carbidic and in the zero-valent state when the reaction is run at low conversions [6],... 

The reaction of benzene with bromine in the presence of an iron catalyst eliminated most of the proposed structures. This reaction produced only one monobromo product and three distinct dibromo products (ortho, meta, and para). 

Chlorination of 2,1,3-benzothiadiazoles can take place either by addition or substitution, depending on the reaction conditions, the nature of the substituents in the benzene ring, and the catalyst employed. The uncatalyzed reaction of (1) with chlorine is exothermic and produces an isomeric mixture of tetrachloro addition products, which form 4,7-dichloro-2,l,3-benzothiadiazole on treatment with base <70RCR923>. In the presence of an iron catalyst, chlorine substitution in the 4,7-positions predominates. 

The new Brownsville, Tex., plant for the manufacture of synthetic liquid fuels from natural gas makes use of this reaction to increase the octane number of its product by as much as 20 units. Synthetic naphtha produced over iron catalyst is highly olefinic and contains substantial amounts of straight-chain isomers with terminal double bonds (8). The shifting of these double bonds toward the center of the molecule may be accomplished by vapor-phase treatment employing synthetic cracking catalyst in the fluid state, under mild catalytic cracking conditions. Oxygenated compounds also present are converted under the isomerization conditions to hydrocarbons and water. 

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