Etude par Spectroscopie et Microscopie Raman de Phases Oxyde de Molybdène Déposé sur Alumines

Abstract

Abstract Raman spectroscopy and microscopy have been used to study some catalysts: Mo supported on alumina. Different Mo species were found, depending upon the amount of molybdenum deposited on the carrier. At low coverages (4% wt MoO 3 ) distorted molybdate tetrahedra were observed. Increasing the surface coverage resulted in the formation of a polymolybdate phase with octahedrally surrounded molybdenum. Additionally, ‘bulk MoO 3 ’ appeared when amounts were above 16% wt MoO 3 . When the supports were washed during their preparation with aqueous NH 4 OH and HNO 3 solutions, preferential formation of polymolybdate phase was observed. In case of washing with alkaline solution ‘free MoO 3 ’ was also detected. Finally using the Raman microprobe MOLE, a map giving the distribution of the different species at the surface of support was obtained.