Magnetite catalyst

Huff, G. A., Jr., and Satterfield, C. N. 1984. Intrinsic kinetics of the Fischer-Tropsch synthesis on a reduced fused-magnetite catalyst. Ind. Eng. Chem. Process Des. Dev. 23 696-705. 

Still following the macro-structural hypothesis which we favored at that time, we abondoned the idea of a specific favorable influence of flux promoters and assumed instead that the cause for the success of the magnetite experiment was the compact porous structure of the iron sponge which was formed in the test oven by the reduction of the Swedish ore. An apparent support of this idea was that contrary to the favorable action of the dense iron sponge obtained from magnetite, catalysts of a looser structure such as, e.g., iron asbestos preparations had always been particularly ineffective. 

Catatyat Fusmt Promoted Magnetite Catalyst Cappsrrarw/AlumWum... 

The first application in 1992 used a two-bed, hot-wall KAAP reactor that featured a low pressure drop and radial flow. Because of the KAAP catalyst s high activity, thin beds are necessary to keep operating temperatures within the desired range203. In 2002 the KAAP reactor had evolved to a four-bed design. A magnetite catalyst is used in the first bed of the synthesis loop when the ammonia concentration is below 2% of the feed. Then the ruthenium catalyst is used in the next three beds to bring the ammonia level up to 18% or more215. 

In the Haber-Bosch process, ammonia is formed from the reaction between N2 and H2, using a Fe304 (magnetite) catalyst promoted with A1203, CaO, K20 and a moderately small amount of iron and other elements [25], In this mixture, the catalytically active... 

With a reduced fused magnetite catalyst a substantial gas-to-liquid mass transfer resistance can be encountered, which causes the paraffin-to-olefin ratio of the hydrocarbon products to decrease. 

With an active reduced fused magnetite catalyst in a stirred autoclave reactor we have shown that substantial mass transfer resistances are readily encountered that can greatly lower the... 

Under intrinsic-kinetic conditions the carbon number distribution of products from a reduced fused magnetite catalyst Is not significantly affected by wide variations In H, and CO concentration and mass-transfer resistances have no noticeable effect, as would be expected. To the extent that other selectlvltles, such as oxygenate product composition, are governed by H and CO concentrations In the liquid, we would similarly expect to observe effects caused by mass transfer, although this was not done here. Likewise with other catalysts, such as cobalt, which appear to be more sensitive to reaction conditions and to secondary reactions, more marked effects from significant mass transfer reactions are anticipated. 

Figure 6 Relative magnetite catalyst concentration for the first (+) and second ( ) stage reactor catalyst bed...

Description The key features of the KBR Purifier Process are mild primary reforming, secondary reforming with excess air, cryogenic purification of syngas, and synthesis of ammonia over magnetite catalyst in a horizontal converter. 

The group of metals forming low-stability or unstable nitrides includes Mn, Fe, Co, Ni, Tc and Re. As in the case of iron a clear structural sensitivity was found for rhenium but the role of promoters remains the subject of discussion. There are also indications of structure sensitivity for cobalt and nickel. It was attempted to improve the activity of the classical magnetite catalyst by alloying with nickel or cobalt. The only commercial catalyst is a cobalt containing magnetite [392],... 

When a series of silica supported-magnetite catalysts of varying iron oxide particle size were investigated, it was determined that Si substitutes into the magnetite lattice according to the following reaction(49) ... 

The effect of Si substitution on the turnover frequency for WGS is shown in Figure 11. The turnover frequencies plotted in this figure were based on the magnetite surface area as determined by the NO chemisorption technique. The turnover frequencies shown for unsupported Fe O indicate that the factor of 10 decline in activity for the silica-supported catalysts is not a particle size effect, but instead is a consequence of the substitution of Si into the lattice. However, when the adsorption of CO/COo at 663 K was used to titrate the surface sites instead of NO, the resulting turnover frequencies were essentially constant as shown in Figure 12. Accordingly, the CO/CO2 mixture apparently titrates the sites active for WGS. Clearly, the number of active sites is decreased markedly as the particle size decreases in the silica-substituted magnetite catalysts. 

In closing, it is important to note that the CO/CO2 adsorption technique effectively titrates the active sites for WGS on magnetite catalysts which differ in activity by over an order of magnitude. Nitric oxide on the other hand titrates all of the surface cation sites and is unaffected by Si-substitution. Indeed, NO is known to chemisorb strongly on iron oxides and may even be able to reconstruct the surface. Thus, the combined use of NO and CO/CO2 adsorption provides information about the total magnetite surface area and fraction of the magnetite surface which is active for the WGS reaction. 

Huff GA, Satterfield CN (1984) Intrinsie kineties of the Fiseher-Tropseh synthesis on a reduced fused-magnetite catalyst. Ind Eng in Chem Prod Res Develop 23 851-954 Humayun M, Clayton R (1995) Potassium isotope cosmochemistiy—genetic-implications of volatile element depletion. Geoehim Cosmoehim Acta 59 2131-2148 Igunmov SA (1976) Sulfur isotope exchange between sulfide and sulfate in hydrothermal solutions. Geokhimiya 4 497-503... 

V. Subramanian, D.-W. Jeong, W.-B. Han, W.-J. Jang, J.-O. Shim, H.-S. Roh, Ha production from high temperature shift of the simulated waste derived synthesis gas over magnetite catalysts prepared by citric acid assisted direct synthesis method, Int. J. Hydrogen Energy 38 (2013) 8699-8703. 

Rethwisch and Dumesic [5] studied the adsorption of CO/CO2 and CO/CO/ H2O gas mixtures over iron oxide catalysts and concluded regarding the regenerative mechanism in the magnetite catalysts. In 1982 Lund and Dumesic [6] concluded that catalysts that are not active for adsorption of CO and CO2 are not active for water gas shift (WGS). Tinkle and Dumesic [7] performed... 

C. R. F. Lund, J. A. Dumesic, Strong oxide-oxide interactions in silica-supported magnetite catalysts IV. Catalytic consequences of the interaction in water-gas shift, J. Catal. 76 (1982) 93-100. 

Different reduction procedures apply if the catalyst is prereduced or when a combination of prereduced and unreduced catalyst is used. Whereas reduction of the bulk magnetite catalyst goes on over days, the reduction of the superficial oxidic layer of the prereduced catalyst is facile and may be accomplished within approximately one day if solely prereduced catalyst is charged. Often the first bed is charged with prereduced catalyst to enable fast reduction and onset of the ammonia synthesis reaction, which thereby liberates heat to support the endothermic reduction in the remaining part of the bed. 

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