Iron catalysts behavior

Niemantsverdriet, J. W., and van der Kraan, A. M. 1981. On the time-dependent behavior of iron catalysts in Fischer-Tropsch synthesis. J. Catal. 72 385-88. 

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],... 

CO oxidation, 28 108 iron catalyst, 30 168 kinetics, 28 250-257 complicated, 28 257-263 latest developments in, 5 1 over amorphous metal alloys, 36 372-374 over iron, 36 24-25 on alumina support, 36 47 antipathetic behavior, 36 150, 152 particle size and, 36 131-132 promotion by potassium, 36 36-37 over rhenium. 36 24-25 promotion by potassium, 36 37 photocatalysis over perovskites, 36 304 Anunoxidation, 30 136-137 allyl alcohol, 30 157-158... 

At the Mellon Institute he applied l4C tracers to examine the behavior of intermediates in Fischer-Tropsch synthesis over iron catalysts. By adding small amounts of radioactively labeled compounds to the CO/H2 synthesis gas mixtures, he was able to prove that some of these compounds (e.g., small alcohols) are involved in the initiation step of the chain growth process that leads to larger hydrocarbon products. It was during this era that his associates first placed a catalytic reactor into the carrier gas stream of a gas chromatograph and developed the microcatalytic pulse reactor, which is now a standard piece of equipment for mechanistic studies with labeled molecules. While at Mellon Institute Emmett began editing his comprehensive set of seven volumes called Catalysis, which he continued at Hopkins. 

Niemantsverdriet JW, Van der Kraan AM, Van Dijk WL, Van der Baan HS. Behavior of metallic iron catalysts during Fischer-Tropsch synthesis studied with Mossbauer-spectroscopy, X-ray-diffraction, carbon content determination, and reaction kinetic measurements. J Phys Chem. 1980 84(25) 3363-70. 

Poisoning of iron catalysts during ammonia synthesis by sulfur compounds has received relatively little attention (154, 240-244). Nevertheless, the previous work provides information on the poisoning mechanism and interesting examples of how oxide promoters may influence the sulfur poisoning behavior of a catalytic metal. 

J.W. Niemantsverdriet, A.M. van der Kraan, W.L. van Dijk, and H.S. van der Baan, Behavior of Metallic Iron Catalysts During Fischer-Tropsch Synthesis Studied with Mossbauer Spectroscopy, X-ray Diffraction, Carbon Content Determination, and Reaction Kinetic Measurements, J. Phys. Chem. 84 (1980) 3363. 

Comparison of the behavior of alcohol in the presence of an iron catalyst at ordinary pressures and at high pressures showed that in the former case the reaction occurs at a lower temperature and also that for any given temperature the velocity of reaction is much greater.59 That is, pressure appeared to decrease the decomposition. At ordinary pressures in the presence of an iron catalyst, alcohol decomposes rapidly at temperatures between 510° and 525° C. to give principally acetaldehyde and gases rich in hydrogen. Above 525° C. increases in temperature are accompanied by corresponding decreases in aldehyde production and increases in the quantity of solid carbon deposited on the iron reactor walls. 

Addition of copper seems to have an important effect on the behavior of iron catalysts. Just as in the case of cobalt, the addition of copper lowers the reduction temperature for iron. However, the effect of copper on the life of the iron catalyst is not as adverse as on cobalt. 

It is known that the conditions of the reduction are important to the behavior of ammonia type iron catalysts during the synthesis of hydro-... 

The work of the Bureau of Mines is devoted to the behavior of cobalt and iron catalysts, and particularly to questions concerning the reaction mechanism and the relationship between catalyst composition and synthesis reaction. 

Cobalt and nickel catalysts convert the oxygen of the carbon monoxide preferentially to water, iron catalysts to carbon dioxide. The different behavior of the iron can not be explained by conversion of primarily produced water with carbon monoxide. The water gas shift reaction can be carried out in the presence of cobalt catalysts as well as in the presence of iron catalysts. The amount of carbon dioxide increases with increasing synthesis temperatures, and also in the presence of cobalt catalysts. 

There are also reports indicating that the surface area and porosity of carbons do not affect either the active-phase dispersion or the catalytic activity. A very important factor influencing active-phase dispersion is the precursor used to prepare it. Rodrfguez-Reinoso et al. [14] used two different iron precursors (iron nitrate in aqueous solution and iron pentacarbonyl in organic solution) to prepare iron catalysts supported on activated carbons with different pore size distributions. They obtained an increase in iron dispersion with the support surface area for the nitrate series, but a high and unaffected dispersion was found for the pentacarbonyl series. These catalysts were used in the CO hydrogenation reaction, where no important differences in catalytic behavior were found for catalysts in both series. 

Hall et al. also converted labeled propanal with the singly promoted iron catalyst at 1 atm conditions. The results showed that its behavior was quite similar to that of 1-propanol, with an incoiporation of about 37 percent. In all respects, the data obtained with propanal were... 

In 1930, Smith, Hawk, and Golden (16) discovered that ethylene, when added to the synthesis gas, enters into the oil-producing reaction on a Co-Cu-MnO catalyst but not on an Fe-Cu catalyst. In the latter case, most of the ethylene appears as ethane in the products. It was pointed out also that water was the main oxygenated product from the cobalt catalyst, whereas carbon dioxide was the chief corresponding product on the iron catalyst. The behavior of ethylene when added to 83mthesi8 gas and passed over a cobalt catalyst was verified by Craxford (17) in 1939. 

It should be clear from this discussion that the working, active, and selective catalyst is a complex, multicomponent chemical system. This system is finely tuned and buffered to carry out desirable chemical reactions with high turnover frequency and to block the reaction paths for other thermodynamically equally feasible but unwanted reactions. Thus, an iron catalyst or a platinum catalyst is composed not only of iron or platinum but of several other constituents as well to ensure the necessary surface structure and oxidation state of surface atoms for optimum catalytic behavior. Additives are often used to block sites. 

It was reported [20, 96] that the counter-ion type on mica influences the polymerization behavior of the supported catalyst Even though micas do not have exactly the same structure of montmoriUonites, they are considered as clay materials and some of their behavior may be translated to montmoriUonites. Hiyama et al. [20] compared ethylene polymerization with an iron catalyst supported on micas with different counterions. They observed that when the polymerization catalyst was supported on M" mica (where M" = Mg, Zn, and Fe " ), polymerization activities were approximately 10-fold higher than those obtained when Na mica was used as a support. Kurokawa et al. [96] supported Cp2ZrCl2 on fluorotetrasUicic micas with different counter ions. During ethylene polymerization, itwas observed that the polymerization activity of the catalyst supported on Na mica (Cp2ZrCl2/... 

Van der Laan [82] reported attempts to model FT in a bubble column reactor. His model exhibited well-mixed liquid and two gas bubble regimes small bubbles that were well mixed and large bubbles that showed plug flow behavior (Figure 12.21). Van der Laan [82] also provided a summary of bubble column reactor models that others have utilized (Tables 12.1 and 12.2). He concluded that the FT slurry bubble column reactor is reaction controlled due to the low activity of the iron catalyst and the... 

In other words, the activity of fused iron catalysts with iron oxides as a precusor relates to not only the content of FeO, but also, more importantly, to its crystal structure of wiistite. When the Fe +/Fe + ratio is smaller than one, although the content of FeO increases the activity decreases, because the crystal structure of wiistite is not yet formed. When the Fe +/Fe + ratio is smaller than 3.15 where the catalyst precursor begins to come to an incomplete structure of wiistite, the activity increases and surpasses strikingly that of the traditional catalyst with Fe +/Fe + at about 0.5. After the Fe +/Fe + reaches five, catalyst precursor forms a complete wiistite structure, while the fused iron catalysts shows its highest activities. Both the activity and reduction behavior are enhanced significantly compared to that of the traditional catalysts. 

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