Introduction of Iron

As early as in the work by Clearfield et al. [18] in 1973, solid-state reactions of Fe , Co , Ni + and Mn chlorides with ammonium (hydrogen) forms of zeolites A, X and Y were studied to demonstrate the phenomenon of SSIE. Those authors monitored the reactions through titration of HCl evolved. More recently, interest in zeolites containing these transition metals, especially cobalt and 

These criteria (i)-(iii) enable us to distinguish between Fe + in extra-frame-work and Fe + in (tetrahedrally coordinated) framework sites. This would even hold if Fe + occurred in tetrahedrally coordinated extra-framework positions. However, in the opinion of Kucherov and SUnkin [148], the occmrence of the anomalous temperature effect strongly suggests that Fe + introduced via SSIE was in fact not located in tetrahedral but rather in distorted octahedral environment, in contrast to the conclusion by Wichterlova et al. [147] (vide supra). 

The interaction of Fe + in Fe,H-ZSM-5 with NH3 and pyridine led to a complete disappearance of the low-field Unes at g2 = 5.65 and g3 = 6.25, and interaction with H2O to their considerable decrease. In any event, the intensity at gi = 4.27 was markedly enhanced. This was especially pronoimced with NHj and pyridine indicating an increase of the crystal field symmetry upon adsorption of these powerfiil Ugands. Interaction with O2 resulted in a considerable but reversible broadening of the Fe + ESR lines caused by dipole-dipole interaction of Fe + with O2. With NHj, the samples of Fe,H-ZSM-5 were reduced at higher temperatures (823 K) as indicated by the disappearance of the signals of Fe + and formation of Fe clusters. Reoxidation did not fiilly restore the original spec-triun. Interaction with p-xylene yielded an ESR spectrum characteristic of p-xylene cation radicals. 

Kucherov and Slinkin also showed that in the solid-state reaction between CuO and Fe,H-ZSM-5 (vide supra) at least 99% of the Fe + ions were replaced by Cu + cations. The ESR signals with g2 = 5.65 and g3 = 6.25 were entirely eliminated, and only a trace of the signal with gi = 4.27 was left. This shows that essentially all of the Fe was in extra-framework positions (vide supra) and no or only negligible insertion of Fe + into the framework had occurred. Thus, SSIE of FeCl3 and H-ZSM-5 did not result in any isomorphous substitution. 

The conventional ion exchange in aqueous solutions of easily oxidizable cations such as, e. g., bivalent Fe, might require the exclusion of oxygen during the whole exchange procedure. This frequently leads to experimental complications that possibly can be avoided by solid-state ion exchange (cf. Cu+, Sect. 5.3.2.1). Therefore, the incorporation of Fe into zeolites via SSIE was 

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With the introduction of iron balls (shot), the same procedure was followed. Hot iron shots were particularly effective against naval sailing vessels. Sometimes, even bullets from small arms were preheated and used as incendiaries... 

In the case of the rare earth metals, it is observed that the 41 electrons are always best described as localizedi HL electrons, which means that the near-neighbor separation Rnn = 2.53J o/ > jBc(4/). On the other hand, Mere are no localized electrons in face-centered cubic palladium (although introduction of iron atoms into the structure induces localized moments on the neighboring palladium atoms), which means that Rnnn = 2.47/io < Rc( d). This implies that... 

The introduction of iron-zinc catalysts led to the low pressure nthesis of liquid and solid hydrocarbons from CO/Hj in 1925 [19. 20. However, it was found that these catalysts were deactivated rapidly and thus further investigations concentrated on nickel and cobalt catalysts. They led to the introduction of a standardized cobalt-based catalyst for llic normal-pressure synthesis of mainly saturated hydrocarbons at temperatures below 200 C. In 1936, the first four commercial plants went on stream. Until 1945 the Fischer-Tropscit synthesis was carried out in nine plants in Germany, one plant in France, four plants in Japan and one plant in Manchuria. The total capacity amounted to approximately one million tons of hydrocarbons per year in 1943. The catalysts used consisted of Co (1(X) parts), ThO (5 parts). MgO (8 parts), and kieselgur (200 parts) and were prepared by precipitation of the nitrates. These catalysts were used in fixed-bed reactors at normal or medium pressures (< 10 bar) and produced mainly saturated straightproduct obtained consisted of 46% gasoline. 23% diesel oil, 3% lubricating oil and 28% waxes (3.15). 

Successful ammonia conversion required discovery of a catalyst, which would promote a sufficiently rapid reaction at 100-300 atm and 400-500°C to utilize the moderately favorable equilibrium obtained under these conditions. Without this, higher temperatures would be required to obtain sufficiently rapid rates, and the less favorable equilibrium at higher temperatures would necessitate higher pressures as well, in order to obtain an economic conversion to ammonia. The original synthesis experiments were conducted with an osmium catalyst. Haber later discovered that reduced magnetic iron oxide (Fe304) was much more effective, and that its activity could be further enhanced by the presence of the promoters alumina (AI2O3 3%) and potassium oxide (K2O 1%), probably from the introduction of iron lattice defects. Iron with various proprietary variations still forms the basis of all ammonia catalyst systems today. 

The luminescent properties of zinc sulphide phosphors change considerably with the introduction of iron into the crystal. In particular, if the iron... 

The introduction of iron in the lattice of zeolite topologies such as MFI and CFI is performed via direct synthesis and post-synthetic modification. Dinuclear iron clusters in appropriate zeolites realize oxidation of methane into methanol at room temperature after N2O activation. Both mono and dinuclear iron coordination and lattice coordination is treated with theory and experiment. In FeCIT-5 and Fe-ZSM5 are made by over-exchange via sublimation of iron salts in Al-zeolites. When extra-framework iron oxides are made in zeolites, the extraframework iron oxide clusters can be anchored to zeolites. 

Pseudomorphic crystals after primary alite contain fine inclusions or margins of ferrite, belite, and free lime Moderate reduction, and introduction of iron into alite lattice resulting in instability and decomposition (Woermann, 1960)... 

Catalysts which are doped with foreign ions in order to modify their activity have been prepared traditionally by impregnation of the solid support or by coprecipation followed by controlled thermal treatment Similar methods have been adopted also in the preparation of iron-titanium (IV) oxide photocataiysts in which the introduction of iron as iron (111) species has resulted in the enhancement of the activity of the solids in the photocatalytic reduction of dinitrogen by water vapour 11,231-... 

Iron Fertilization of the Oceans. The intentional introduction of iron into the upper layers of certain areas of the ocean to encourage phytoplankton blooms is a form of CDR. The concept rehes on the fact that increasing certain nutrients—such as iron— in nutrient-poor areas stimulates phytoplankton growth. Carbon dioxide is absorbed from the surface of the ocean during the processes of photosynthesis when the phytoplankton, marine animals, and plankton die and sink in the natural cycle, that carbon is removed from the atmosphere and sequestered in the ocean s depths. 

The influence of high-thermal treatment could be explained by the enhancement of iron cation mobility, which facilitated the introduction of iron cations into channels resulting in the formation of a-sites. The concentration and strength of protonic acidic sites significantly influences the rate of deactivation of Fe-ZSM-5 catalysts. 

There are only a few Mossbauer nuclei which are interesting in zeolite chemistry and, thus, candidates for application of Mossbauer spectroscopy in soUd-state ion exchange. However, among them is one of the most important elements, viz., iron, which has also attracted much attention in zeoUte chemistry as a key component of possible catalyst formulations. Mossbauer spectroscopy proved to be exceptionally successful in discriminating Fe + and Fe + cations residing on extra-framework sites after introduction of iron via soHd-state ion exchange. Moreover, Mossbauer spectroscopy provides information about the various coordinations of Fe + and Fe in zeoUte lattices (cf. Sect 5.3.4). 

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