Thermal stability and reactivity in oxygen of potassium ferrites with spinel structure

Abstract

The potassium content really incorporated in the spinel lattice of the magnetite determined by thermogravimetric analysis in vacuum or in oxygen was about 2.45 wt%. In spite of this low content, the potassium strongly stabilises the defect spinel structure resulted by the potassium-substituted magnetite oxidation and increases the transformation temperature of the defect phases into a-Fe203 or KFe11017.In present study on the reactivity in oxygen of finely divided ferrites with spinel structure [1, 2] we present the results of studies on the thermal stability and the behaviour in oxygen of potassium doped magnetites with large specific areas enabling finely divided substituted magnetites and nonstoichiometric ferrites with fl-alumina-like structure to be formed. These metastable phases are deemed to have novel interesting physicochemical properties as catalysts for example in the dehydrogenation of ethyl-benzene to styrene due to the redox properties of spinel and defect spinel compounds [3,4].In the past, most of the dehydrogenation catalysts based on Fe-K-O and Fe-M-K-O systems (M = Cr, A1) have been obtained by mechanical mixing of a-Fe203 with potassium salts at calcination temperatures above 1000 ~ [5] and under these conditions, it is difficult to achieve a homogeneous distribution of the doping element, potassium, and to obtain mixed oxides with a John W~ley & Sons, Limited, Chichester Akaddmiai IOad6, Budapest

Incorporation of Cadmium and Nickel into Ferrite Spinel Solid Solution: X-ray Diffraction and X-ray Absorption Fine Structure Analyses

“…This was likely due to the surface area of the sintered SNCBS-600 (7.39 m 2 /g) being greater than those of the Cd x Ni 1– x Fe 2 O 4 samples (ranging from 1.78 to 1.96 m 2 /g) (Table S8). In addition to Cd and Ni, the Co and K concentrations in the leachates also decreased significantly after sintering, potentially indicating the transformation of Co and K into more stable crystal structures. − K has been reported to strongly stabilize defect spinel structures by a potassium-substituted magnetite oxidation process . Moreover, the KFe 11 O 17 and NaFeO 2 phases were formed herein after sintering (Figure ).…”

“…39−41 K has been reported to strongly stabilize defect spinel structures by a potassium-substituted magnetite oxidation process. 39 Moreover, the KFe 11 O 17 and NaFeO 2 phases were formed herein after sintering (Figure 5). NaFeO 2 is highly soluble in aqueous (eq 9) or acidic media.…”