Supported Iron oxide particles

Characterization of Supported Iron Oxide Particles Using Mdssbauer Spectroscopy and Magnetic Susceptibility... 

PHILLIPS ETAL. Supported Iron Oxide Particles... 

Burgoyne and Thomas (17G) have passed mixture air through an iron-electrode arc prior to passing into a Bunsen tube. The effect of the minute iron oxide particles contained in the stream is to lower the lean limit of flammability of hydrogen. Sanger (33G) deals with such topics as the dependency of combustion on pressure, temperature, and the moisture content of powders, and gives a series of equations in support of his hypothesis. 

Microcrystalline cellulose (Merck) appears to have been used most successfullybut even this support matrix should be used with continuous mixing to maintain adequate suspension. The inclusion of a nonionic detergent in the incubation mixture (0.5% v/v Tween-20 - 0.1% v/v Brij-35 ) helps to keep the particles dispersed and to reduce nonspecific binding. Other aproaches and matrices used with variable success have included conjugation to iron oxide particles coated with polymerized w-diaminobenzene, adsorption to individual polystyrene balls 6.4 mm in diameter, and adsorption to polystyrene plastic tubes. 

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) ... 

Accordingly, van den Brink [37] demonstrated that impregnation with a solution of iron(III) ammonium citrate and iron(III) gluconate resulted after drying in a uniform distribution of the active precursor within the support body. Transmission electron microscopy of the subsequently calcined catalysts displayed the presence of very small iron oxide particles, homogeneously dispersed over the silica. With impregnation of iron(ni) ammonium EDTA, the pH of the impregnating solution is important. A solution of a pH of 5.3 produced an egg-shell distribution, and a solution of pH 7.1, a faint egg-shell. However, solutions of a pH of above 8.5 led to uniform... 

XPS was used to determine the iron oxidation state and the dispersion of the applied iron phase of the iron-on-zirconia catalysts. As expected, iron was found to be in the trivalent state. Dispersion calculations (performed as published elsewhere [17]) indicated that no significant difference in dispersion was obtained when using either different precursors, or different supports, and whether or not applying a thermal pre-treatment. The iron oxide particle sizes calculated according to the procedure of Kuipers et a/. [18] range from 100 to 150A, which is smaller than found with XRD. This can be explained, however, when taking the specific sensitivities of XPS and XRD into account. 

The stabilization of the iron oxide particles by supports prepared at pH levels of 3 and 8 seemed to be different. Bare AIPO4 supports precipitated at a pH of 8 displayed a higher stability than AIPO4 supports precipitated at a pH of 3. The decrease of the specific surface area of the support resulted in sintering of the iron oxide particles too. A higher thermal stability was also obtained by increasing the Al/P ratio. The absorbent with a support of an Al/P ratio of 1.9 showed no diffraction pattern, indicating very small iron oxide particles, in contrast to the use of supports with an Al/P ratio of 0.7. 

Nitrogen adsorption experiments showed a typical t)q5e I isotherm for activated carbon catalysts. For iron impregnated catalysts the specific surface area decreased fix>m 1088 m /g (0.5 wt% Fe ) to 1020 m /g (5.0 wt% Fe). No agglomerization of metal tin or tin oxide was observed from the SEM image of 5Fe-0.5Sn/AC catalyst (Fig. 1). In Fig. 2 iron oxides on the catalyst surface can be seen from the X-Ray diffractions. The peaks of tin or tin oxide cannot be investigated because the quantity of loaded tin is very small and the dispersion of tin particle is high on the support surface. 

Suppose you prepared an iron oxide catalyst supported on an alumina support. Your aim is to use the catalyst in the metallic form, but you want to keep the iron particles as small as possible, with a degree of reduction of at least 50%. Hence, you need to know the particle size of the iron oxide in the unreduced catalyst, as well as the size of the iron particles and their degree of reduction in the metallic state. Refer to Chapters 4 and 5 to devise a strategy to obtain this information. (Unfortunately for you, it appears that electron microscopy and X-ray diffraction do not provide useful data on the unreduced catalyst.)... 

As already indicated, the difficulty of reducing supported iron in hydrogen is well-known [6,8,11]. It probably arises from a combination of causes, the two most important of which are a strong interaction with the support [6,8] and reoxidation or inhibition by water vapour in the pores of the oxide [14]. With MgO as support, there is undoubtedly a strong tendency for iron, especially at the Fe2+ stage of reduction, to be present at least in part as FeO-MgO (Fe Mgi.jjO) solid solution [6,8]. This need not be deleterious to the ultimate formation of finely-divided iron, provided the method of preparation has led to a solid solution in which the Fe2+ ions are well-distributed. The iron particles are limited in size... 

The electron interaction between nanosized gold particles and iron oxide support is only one factor which determines the properties of the gold/oxide system. For instance, in the Au/FeO,c/Si02/Si(l 0 0) model sample the depth profile (after successive Ar ion bombardment at a... 

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