MOESSBAUER STUDY OF SUPPORTED IRON AND MANGANESE CATALYSTS.

Mossbauer Effect Spectroscopy was used in conjunction with x-ray diffraction catalysts in order to obtain a better understanding of the role of manganese and the effect of the support on these bimetallic catalysts. This study was carried out on the bimetallic catalysts iron-manganese supported on alumina or silicalite with different percentages of loading and under various treatments (calcination, reduction, carburization, and during Fischer-Tropsch reaction). In the cases of a pure iron catalyst and unsupported iron-manganese catalysts, the oxidation state was identified from x-ray diffraction and Mossbauer spectroscopy as (alpha)-Fe(,2)O(,3) with hyperfine fields of 511 (+OR-) 3 kOe, 508 (+OR-) 3 kOe, and 504 (+OR-) kOe, and particle sizes of 350 (+OR-) 10 (ANGSTROM), 250 (+OR-) 10(ANGSTROM), and 240 (+OR-) 10(ANGSTROM) for the pure iron catalysts, 50% Fe-50% Mn and 40% Fe-60% Mn catalysts, respectively. The oxided state could be completely reduced to (alpha)-Fe in the case of the pure iron catalysts. In the case of the bimetallic iron-manganese catalysts, the reduced state revealed the presence of Fe(\u272+) and Fe(\u273+) in addition to (alpha)-Fe. The carbided state before and after the Fischer-Tropsch reaction indicates the presence of (chi)-Fe(,5)C(,2). The role of the support in these bimetallic catalysts was pronounced from the first stages of treatment. In the case of alumina support, the oxided state of the pure iron catalyst (15% Fe/alumina) has been identified as (gamma)-Fe(,2)O(,3) based on x-ray diffraction and Mossbauer spectroscopy results with a particle size of 135 (+OR-) 10(ANGSTROM). As a result of the strong reaction between the metal and the support, the oxided state could be reduced only up to 50% with the remainder Fe(\u272+) and Fe(\u273+). The carbided state could be identified as (chi)-Fe(,5)C(,2) with a surface area of 55 (+OR-) 1 m(\u272)g. In the case of silicalite support, the oxided state of the pure iron catalyst (15% Fe/85 silicalite) has been identified as (alpha)-Fe(,2)O(,3) using x-ray diffraction and Mossbauer spectroscopy which could be reduced completely after only 2 hr at 673(DEGREES) K. The addition of manganese to the pure iron supported catalysts gave a different result, depending on the type of support. In the case of the silicalite support, by increasing the percentage of manganese (from 7.5 wt% to 9 wt%), the oxided state could be reduced up to 75% after 30 hr of reduction in H(,2) at 673(DEGREES)K, and could be carburized completely to (chi)-Fe(,5)C(,2) after Fischer-Tropsch reaction. In the case of the alumina support, the oxided state of the bimetallic catalyst (7.5 Fe-7.5 Mn) and (6 Fe-9 Mn) could not be even partially reduced to Fe(DEGREES). (Abstract shortened with permission of author.)

TEMPERATURE STUDY OF A Cu - 0,2 AT.% Fe ALLOY

Par spectrométrie Mössbauer on a suivi entre 298 K et 919 K la mise en amas, la précipitation et l'oxydation des atomes de fer en fonction du temps et de la température dans un alliage métastable à 0,2 at.% de fer. Une solubilité du fer dans le cuivre de 2000 ppm à 891 ± 10 K a été déterminée. L'oxydation interne du fer se produit au-dessus de 843 K pour un vide d'environ 10-5 torr et conduit à des paramètres hyperfins qui ne sont caractéristiques d'aucun des oxydes suivants : FeO, Fe2O3, Fe2O4, ou CuFeO2.Mössbauer effect spectroscopy has been used to follow the temperature and time dependence of the clustering, precipitation and oxidation of Fe atoms in a metastable Cu-0.2 at.% Fe alloy. Spectra were obtained from 298 K to 919 K in regular intervals. The solubility of Fe in Cu was found to be 2000 at.ppm at 891 ± 10 K. Internal oxidation of the Fe occured above 843 K in a vacuum of about 10-5 torr. The oxidation product has Mössbauer parameters which are not characteristic of FeO, Fe2O3, Fe3O4 or CuFeO2