Redox processes at the surfaces of Fe2O3$z.sbnd;MoO3/SiO2 catalysts

Mössbauer and catalytic measurements have been carried out on Fe2O3MoO3 supported on silica with different surface areas. The Mössbauer study of the catalyst reducibility (using methanol) and reoxidizability at high temperature has indicated that, as a consequence of the interaction between the support and the active species, both Fe and Mo enter the silica. This process, however, is limited to the surface of the support where the iron valence and coordinations are stabilized. Supported iron-molybdate can form only on this film. The comparative analysis of the Mössbauer and the catalytic data indicates that the high activity and selectivity, observed for catalysts with low surface areas, is connected with the presence of an iron-molybdate thin film. For high areas the iron-molybdate destruction determines the lower activity and selectivity.