IN-SITU MOSSBAUER SPECTROSCOPIC STUDY OF IRON SITE EVOLUTION IN IRON AND COBALT MOLYBDATES CATALYSTS IN PROPENE OXIDATION REACTION CONDITIONS

被引:23
作者
BENAICHOUBA, B
BUSSIERE, P
VEDRINE, JC
机构
[1] UNIV LYON 1,INST RECH CATALYSE,CNRS,F-69626 VILLEURBANNE,FRANCE
[2] ECOLE NORMALE SUPER,SPECT MAT LAB,MOSTAGANEM 27000,ALGERIA
关键词
IN-SITU CATALYST CHARACTERIZATION; MOSSBAUER SPECTROSCOPY; COBALT MOLYBDATE; IRON MOLYBDATE; PROPENE OXIDATION;
D O I
10.1016/0926-860X(95)00112-3
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
In-situ Mossbauer spectroscopy was used to study FexCo1-xMoO4 molybdates and their mixtures with Bi-2(MoO4)(3) in the 360-415 degrees C range under a flow of a mixture C3H6/O-2/N-2 = 100/100/560 Torr. Ferrous molybdate FeMoO4 was progressively oxidized to ferric molybdate and ferric oxide. Mixed cobalt and iron molybdates Fe-x/Co1-xMoO4 exhibited the following behaviour: (1) for all iron contents, the CY 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 Fe-2(MoO4)(3) was detected and diminished by half under catalytic conditions; (2) when Bi-2(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 Bi-2(MoO4)(3) stabilizes Fe3+ in the solid solution, It is proposed that Fe2+-Fe3+ t pairs take an important place in the mechanism of propene mild oxidation.
引用
收藏
页码:31 / 45
页数:15
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