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In-situ Mössbauer spectroscopic study of iron site evolution in iron and cobalt molybdates catalysts in propene oxidation reaction conditions
In-situ Mössbauer spectroscopy was used to study Fe x Co 1− x MoO 4 molybdates and their mixtures with Bi 2(MoO 4) 3 in the 360–415°C range under a flow of a mixture C 3H 6/O 2/N 2 = 100/100/560 Torr. Ferrous molybdate FeMoO 4 was progressively oxidized to ferric molybdate and ferric oxide. Mixed co...
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Published in: | Applied catalysis. A, General General, 1995-09, Vol.130 (1), p.31-45 |
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Main Authors: | , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that cite this one |
Online Access: | Get full text |
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Summary: | In-situ Mössbauer spectroscopy was used to study Fe
x
Co
1−
x
MoO
4 molybdates and their mixtures with Bi
2(MoO
4)
3 in the 360–415°C range under a flow of a mixture C
3H
6/O
2/N
2 = 100/100/560 Torr. Ferrous molybdate FeMoO
4 was progressively oxidized to ferric molybdate and ferric oxide. Mixed cobalt and iron molybdates Fe
x
Co
1−
x
MoO
4 exhibited the following behaviour: (1) for all iron contents, the α phase spectrum diminished to the benefit of the β phase. The Fe
3+ sites of the solid solution underwent reduction. At high iron content, the Fe
3+ in Fe
2(MoO
4)
3 was detected and diminished by half under catalytic conditions; (2) when Bi
2(MoO
4)
3 was added to Fe
x
Co
1−
x
MoO
4, there was no reduction of Fe
3+ sites in the solid solution. The
α →
β phase transition was not observed in the case of the low and medium iron contents. In the high iron content samples the α-phase spectrum decreased to the expense of the β phase but did not disappear totally after catalytic reaction. It is concluded that cobalt stabilizes Fe
2+ sites in the solid solution while Bi
2(MoO
4)
3 stabilizes Fe
3+ in the solid solution. It is proposed that Fe
2+-Fe
3+ pairs take an important place in the mechanism of propene mild oxidation. |
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ISSN: | 0926-860X 1873-3875 |
DOI: | 10.1016/0926-860X(95)00112-3 |