Iron oxidations, heterogeneous

Dehydrogenation, Ammoxidation, and Other Heterogeneous Catalysts. Cerium has minor uses in other commercial catalysts (41) where the element s role is probably related to Ce(III)/Ce(IV) chemistry. Styrene is made from ethylbenzene by an alkah-promoted iron oxide-based catalyst. The addition of a few percent of cerium oxide improves this catalyst s activity for styrene formation presumably because of a beneficial interaction between the Fe(II)/Fe(III) and Ce(III)/Ce(IV) redox couples. The ammoxidation of propjiene to produce acrylonitrile is carried out over catalyticaHy active complex molybdates. Cerium, a component of several patented compositions (42), functions as an oxygen and electron transfer through its redox couple. 

Let us now include an additional component to the Fe-0 system considered above, for instance S, which is of relevance for oxidation of FeS and for hot corrosion of Fe. In the Fe-S-0 system iron sulfides and sulfates must be taken into consideration in addition to the iron oxides and pure iron. The number of components C is now 3 and the Gibbs phase rule reads Ph + F = C + 2 = 5, and we may have a maximum of four condensed phases in equilibrium with the gas phase. A two-dimensional illustration of the heterogeneous phase equilibria between the pure condensed phases and the gas phase thus requires that we remove one degree of... 

The degradation of the B02 was conducted by using iron oxide catalyst supported on cerium oxide as a heterogeneous Fenton catalyst in the presenee of H2O2. The effect of the... 

Avnir, D. (1989) The fractal approach to heterogenous chemistry. J. Wiley, New York Avnir, D. Farin, D. Pfeifer, P. (1983) Chemistry in noninteger dimension between two and three. II. Fractal surfaces at adsorbens. J. Chem. Phys. 79 3566-3571 Avotins, P.V. (1975) Adsorption and coprecipitation studies of mercury on hydrous iron oxide. Ph.D. Thesis, Stanford University, California, 124 p. 

On the other hand, electrical conduction via mixed-valence states is essential for iron oxides used in electrochemical cells or for the mediation of catalytic reactions at iron oxides used as heterogeneous catalysts. 

Acrolein and Acrylic Acid. Acrolein and acrylic acid are manufactured by the direct catalytic air oxidation of propylene. In a related process called ammoxida-tion, heterogeneous oxidation of propylene by oxygen in the presence of ammonia yields acrylonitrile (see Section 9.5.3). Similar catalysts based mainly on metal oxides of Mo and Sb are used in all three transformations. A wide array of single-phase systems such as bismuth molybdate or uranyl antimonate and multicomponent catalysts, such as iron oxide-antimony oxide or bismuth oxide-molybdenum oxide with other metal ions (Ce, Co, Ni), may be employed.939 The first commercial process to produce acrolein through the oxidation of propylene, however, was developed by Shell applying cuprous oxide on Si-C catalyst in the presence of I2 promoter. 

There is a large class of industrially important heterogeneous reactions in which a gas or a liquid is brought into contact with a solid and reacts with the solid transforming it into a product. Among the most important are the reduction of iron oxide to metallic iron in a blast furnace the combustion of coal particles in a pulverised fuel boiler and the incineration of solid wastes. These examples also happen to be some of the most complex chemically. Further simple examples are the roasting of sulphide ores such as zinc blende ... 

The first measurements of deposition and clearance were those of Albert Arnett (1955), who used heterogeneous particles of iron oxide labelled with 59Fe. In later work, to obtain monodisperse particles,... 

The water gas shift reaction occurs on or within the iron oxide particle and therefore a heterogeneous model is employed using separate balances for the pellets and the reactor. 

The linewidths of the Mossbauer spectra of supported iron oxide microcrystallites are larger than those recorded for iron in well-crystallized compounds and may suggest the superimposition of different quadrupole-split doublets arising from a number of ferric ions in a heterogeneity of sites. 

Several heterogeneous catalysts have been developed for the hydroxylation of alkanes under mild conditions.68,69 One of them is the bi-catalytic system, which combines the ability of palladium to convert hydrogen and oxygen to hydrogen peroxide, with the capability of the iron ions to activate the hydrogen peroxide to hydroxylate hydrocarbons.70 Iron oxide and palladium supported on silica have been used as efficient catalysts for the oxidation of cyclohexane to the alcohol and ketone, via the in situ generation of hydrogen peroxide in an acetone solvent.71... 

Szecsody, J.E. et al., Influence of iron oxide inclusion shape on CoII/IIIEDTA reactive transport through spatially heterogeneous sediment, Water Resour. Res., 34, 2501, 1998b. 

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