CENTRES RESPONSIBLE FOR THE CATALYTIC ACTMTY AND SELECTIVITY OF THE Fe-MO-Bi AND Fe-MO-MO TERNARY SYSTEMS

RBsumB.- Des catalyseurs h base de molybdate de fer avec ou sans excb d'oxydes de MO ou de Bi ont et6 caractQis6s. La reduction de bulk de tous les Bchantillons par le methanol ou le l-butbe porte a la formation de 8-FeMoO4. Dans tous les cas la rkoxydation de bulk a redonnk des Bchantil-lons identiques aux catalyseurs frais calcinb. Des correlations entre activitk catalytique et reduction et rkoxydation de bulk ont et6 proposkes. L'excb de M003 n'a pas d'influence sur l'activitk cataly-tique specifique ni sur les marches de reduction et de rkoxydation. Son importance semble btre li& seulement a des proprietks texturelles. Le 8-FeMo04 ne semble pas etre le composant actif pour l'oxydation du buthe. Les rksultats indiquent que la phase active et selective est due a la migra-tion du Bi dans le molybdate de fer. Abstract.- Fe(II1)-molybdate based catalysts with and without MO and Bi oxides excess have been characterized. Bulk reduction of all the samples implies the formation of 8-FeMoO4 both with methanol and l-butene as reagents. In all cases bulk reoxidation gave back samples equal to the fresh calcined catalysts. Correlations between catalytic activity data and bulk reduction and re-oxidation have been proposed. M003 excess proved to have no influence on the specific acti-vity nor on the steps of bulk reduction and re-oxidation. Its importance seems to be related only to textural properties. 8-FeMo04 seemed not to be the active component for l-butene oxidation. Evidence was drawn that the active and selective phase arises from the migration of Bi within the Fe(II1)-molybdate structure. 1. Introduction.- Th