Mg ferrites

The spectra obtained upon adsorption of 1,3-butadiene over the Mg-ferrite catalyst are reported in Fig. 3. The spectrum obtained is similar to that previously reported for the adsorption of 1,3-butadiene over a-Fe203 [19]. The detection of the symmetric C=C stretching mode at 1636 cm (IR inactive in the gas) shows that the molecule is either in the non-centrosymmetric s-cis configuration, or its symmetry is strongly lowered by interaction with... 

Our previous studies concerning hydrocarbons oxidation over transition metal oxides allowed us to conclude that most hydrocarbon molecules are activated at their weakest C-H bond by oxidation occurring at the expense of high-oxidation-state transition metal cations exposed at the catalyst surface, giving rise to surface alkoxides [8]. It is likely that this also occurs on the surface Fe cations on Mg-ferrite surfaces, with a mechanism that can be described as in the following scheme. 

The production of 1,3-butadiene needs catalysts that cannot adsorb butadiene strongly. Actually, this occurs on Mg ferrite and distinguishes the behavior of this material from that of vanadia-based catalysts, that allow the oxidation of butenes to maleic anhydride and actually adsorb butadiene strongly [12]. Our data suggest that the predominant pathway to total oxidation is competitive with respect to the key alkoxide elemination step, more than successive to it, over MgFe204. 

Kimura, T., Ichikawa, M. Yamaguchi, T. (1977). Effects of grain size on cation ordering in sintered Mg-ferrites. Journal of Applied Physics, 48,5033-7. 

Fig. 4.18. The inverse susceptibility of Mg ferrite as a function of temperature for r > Tq, referred to one mole of Fe. The solid line and 6p correspond to Eq. (4.33). (Adapted from Cullity, 1972 data from Serres, 1932 curve constants from Neel, 1948.)...

The activity of Fe is decreased by addition of Ni [78, 79], and a Mn-Fe alloy of 30-40 percent Mn gives a high activity [80]. The conventional promoted iron catalyst is further promoted by the addition of Co. The catalysts are prepared by burning a Fe-Co alloy in O2 followed by the addition of promoters [81]. The alloying effect of Fe-Co, and Fe-Ni was studied in detail [82]. The addition of 3-7 wt% RUO2 to a catalyst composed of Co ferrite (25-35%), Mg ferrite (20-25%), K2O (0.5-2%), and Fe oxide (rest%) increases the ammonia activity and heat resistance of the catalyst [83]. 

Sintered and sprayed ceramic anodes have been developed for cathodic protection applications. The ceramic anodes are composed of a group of materials classified as ferrites with iron oxide as the principal component. The electrochemical properties of divalent metal oxide ferrites in the composition range 0- lA/O-0-9Fe2O3 where M represents a divalent metal, e.g. Mg, Zn, Mn, Co or Ni, have been examined by Wakabayashi and Akoi" . They found that nickel ferrite exhibited the lowest consumption rate in 3% NaCl (of 1 56 g A y at 500 Am and that an increase in the NiO content to 40mol 7o, i.e. O NiO-O-bFejO, reduced the dissolution rate to 0-4gA y at the expense of an increase in the material resistivity from 0-02 to 0-3 ohm cm. 

The structure of so-called hexagonal ferrite is based on the spinel (MgAljOJ structure. Arrangement of oxygen in spinel is CCP, and Mg and... 

Ferrites having a square hysteresis loop (e.g. (Mg, Mn, Zn) Fe204), developed for the now outdated computer core memories, have found applications in the form of a toroidal saturable inductor for regulating the output currents in switched-mode power supplies. 

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