Iron nitrides synthesis

Iron Nitrides as Fischer-Tropsch Catalysts Robert B. Anderson Hydrogenation of Organic Compounds with Synthesis Gas Milton Orchin The Uses of Raney Nickel Eugene Lieber and Fred L. Morritz... 

As to efforts to carry out ammonia synthesis in a technical direction, studies along that line had been started in the B. A. S. F. after Wilhelm Ostwald had suggested such work in 1900. In laboratory experiments considerable yields of synthetic ammonia had been obtained by W. Ostwald (27). However, all attempts to reproduce these yields on a larger scale were futile, and finally Ostwald had to admit that in his original experiments, ammonia had probably been erroneously introduced into the synthesis reactor with a foreign source, presumably in form of an iron nitride, which had been formed by a previous treatment of the iron catalyst with ammonia. 

The reasoning which led the author to make this first shot in the dark regarding the usefulness of combinations of solid compounds as ammonia catalysts was as follows If we assume that a labile iron nitride is an interminate in the catalytic ammonia synthesis, every addition to the iron which favors the formation of the iron nitride ought to be of advantage. In other words, the hypothesis was used that surface catalysis acts via the formation of intermediate compounds between the catalyst and one or more of the reactants. An experimental support for this theory was the fact that a stepwise synthesis via the formation and successive hydrogen reduction of nitrides had been carried out with calcium nitrides (Haber), and cerium nitrides (Lipski). Later, the author found molybdenum nitride as being the best intermediate for such a stepwise synthesis. 

FIGURE 5 Characterization of iron ammonia synthesis catalyst. High-resolution laboratory diffraction indicated a reversible modification of the iron (111) line profile. Under catalytic reaction conditions, a sub-nitride with x = 15-18 is present in addition to the bulk iron matrix. The fitting and assignment of the data were substantiated by observations of the line profile during step changes in the composition of the gas atmosphere. Details and references are given in the text. 

In the case of the ammonia synthesis, iron nitrides instead of carbides were identified. in spent catalysts (Fe4N, Fe3N, and Fe2N). 

Anderson, Schults, Seligman, Hall, and Storch (74) studied the behavior of iron nitrides as catalysts for hydrocarbon synthesis. The e-phase nitrides which have the same crystal structure as the hexagonal Fe2C have a similar favorable influence on catalyst activity. The nitrides are gradually converted to the corresponding carbon compounds. Nitrided catalysts are more resistant to oxidation and the formation of free carbon. These factors may be important for a longer life of these catalysts (75). 

The Synol and isosynthesis processes, as well as the Oxyl and iron nitride variations of the Fischer-Tropsch synthesis, were developed to produce special products from synthesis gas. All but the isosynthesis are designed to produce high yields of oxygenated materials. The isosynthesis yields highly branched aliphatic hydrocarbons and aromatics. While none of these processes has been used commercially, they could be of interest at some future time. 

Tanaka, T., Tagawa, K., and Tazaki, A., Synthesis and magnetic properties of iron nitride particles, Nippon Kagaku Kaishi, 930 (1984). 

Chain Growth and Iron Nitrides in the Fischer-Tropsch Synthesis... 

Developments in the Fischer-Tropsch synthesiis at the Bureau of Mines from 19 5 to I960 include a simple mechanism for chain growth and the use of iron nitrides as catalysts. The chain-growth schene can predict the carbon-number and isomer distributions for products from most catalysts with reasonable accuracy using only 2 adjustable parameters. Iron nitrides are active, durable catalysts that produce high yields of alcohols and no wax. During the synthesis, the nitrides are converted to carbonitrides. 

In research on the Fischer-Tropsch synthesis, FTS, at the Bureau, mechanisms of the growth of the carbon chain and the use of iron nitrides as catalysts were developments that were not anticipated by previous German work. Herington (2) in 1946 was the first to consider chain growth in FTS. He defined a probability 3 that the chain will desorb rather than grow at the surface, where... 

This structure is very similar to that of the (002) plane of (bulk) Fe4N and hence no reconstruction and the assignment of surface nitride. (It should be noted that the known bulk iron nitrides will never be thermodynamically stable under the conditions of ammonia synthesis but may be readily formed in NH3/H2 mixtures providing high virtual N2 pressures.)... 

German chemist in catalysis. He obtained a doctorate in chemical philosophy at Leipzig University nnder the supervision of Bodenstein after twists and turns. In 1904, he joined BASF and studied on ammonia synthesis as an assistant of Bosch. He noticed in study of iron nitrides that trace components changed catalytic performance dramatically and conducted studies of multi-component catalysts. He is a genius who found the doubly promoted iron catalysts only in more year. Haber and Bosch were awarded Nobel Prize for their contribntion to the technology of ammonia synthesis. It should be noted that the contribntion of Mittasch was no less than those of them. 

There is very different behavior for the two-type adsorption states. For instance, H-type nitrogen has no effect on CO adsorption, while L-type nitrogen inhibits CO adsorption. L-type is more active for ammonia synthesis than H-type. If iron nitride was hydrogenated to ammonia, the formation rate of ammonia was also proportional to P, indicating that the H-tjrpe adsorption state of nitrogen is similar to that on iron nitride, i.e., one nitrogen atom is coordinated with several iron atoms,... 

Winter [4] determined the rate of NH3 decomposition on an iron foil at atmospheric pressure in the temperature range 500 to 700 °C. The experiments were carried out in the presence of excess H2 in order to avoid the formation of iron nitride. Many earlier studies had used pure NH3, thereby transforming the catalyst into a nitride phase and making it drastically different from the catalyst under synthesis conditions. 

Emmett and Love [8] found that hydrogenation of iron nitride takes place at temperatures below that of synthesis, which suggests that the hydrogenation of adsorbed nitrogen is fast. 

The reverse reaction to ammonia synthesis, the decomposition to nitrogen and hydrogen, is used in die nitriding of iron and canied out industiially at temperatures around 800 K and atmospheric pressure to produce surfacehardening. This dissolution reaction must also play a part in the synthesis of ammonia by the industiial process. The attempt to ninide non by reaction with nin ogen gas is vety slow under atmospheric pressure, presumably due to the stability of the nitrogen molecule. 

Iron has a rich surface coordination chemistry that forms the basis of its important catalytic properties. There are many catalytic applications in which metallic iron or its oxides play a vital part, and the best known are associated with the synthesis of ammonia from hydrogen and nitrogen at high pressure (Haber-Bosch Process), and in hydrocarbon synthesis from CO/C02/hydrogen mixtures (Fischer-Tropsch synthesis). The surface species present in the former includes hydrides and nitrides as well as NH, NH2, and coordinated NH3 itself. Many intermediates have been proposed for hydrogenation of carbon oxides during Fischer-Tropsch synthesis that include growing hydrocarbon chains. 

Molybdenum In its pure form, without additions, it is the most efficient catalyst of all the easily obtainable and reducible substances, and it is less easily poisoned than iron. It catalyzes in another way than iron, insofar as it forms analytically easily detectable amounts of metal nitrides (about 9% nitrogen content) during its catalytic action, whereas iron does not form, under synthesis conditions, analytically detectable quantities of a nitride. In this respect, molybdenum resembles tungsten, manganese and uranium which all form nitrides during their operation, as ammonia catalysts. Molybdenum is clearly promoted by nickel, cobalt and iron, but not by oxides such as alumina. Alkali metals can act favorably on molybdenum, but oxides of the alkali metals are harmful. Efficiency, as pure molybdenum, 1.5%, promoted up to 4% ammonia. 

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