In-situ Mossbauer spectroscopic study of iron site evolution in iron and cobalt molybdates catalysts in propene oxidation reaction conditions
مقال من تأليف: Benaichouba, B. ; Bussiere, P. ; Vedrine, J. C. ;
ملخص: In-situ Mossbauer spectroscopy was used to study FexCo1-xMoO4 molybdates and their mixtures with Bi2(MoO4)3 in the 360-415[deg]C range under a flow of a mixture C3H6/O2/N2 = 100/100/560 Torr. Ferrous molybdate FeMoO4 was progressively oxidized to ferric molybdate and ferric oxide. Mixed cobalt and iron molybdates FexCo1-xMoO4 exhibited the following behaviour: (1) for all iron contents, the [alpha] phase spectrum diminished to the benefit of the [beta] phase. The Fe3+ sites of the solid solution underwent reduction. At high iron content, the Fe3+ in Fe2(MoO4)3 was detected and diminished by half under catalytic conditions; (2) when Bi2(MoO4)3 was added to FexCo1-xMoO4, there was no reduction of Fe3+ sites in the solid solution. The [alpha] --> [beta] phase transition was not observed in the case of the low and medium iron contents. In the high iron content samples the [alpha]-phase spectrum decreased to the expense of the [beta] phase but did not disappear totally after catalytic reaction. It is concluded that cobalt stabilizes Fe2+ sites in the solid solution while Bi2(MoO4)3 stabilizes Fe3+ in the solid solution. It is proposed that Fe2+-Fe3+ pairs take an important place in the mechanism of propene mild oxidation.
لغة:
إنجليزية