Structure of MoO 3/Al 2O 3-SiO 2 catalysts

• Published in: Applied catalysis Vol. 69; no. 1; pp. 205 - 220
• Main Authors: Henker, Matthias, Wendlandt, Klaus-Peter, Valyon, J., Bornmann, Peter
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1991
• Subjects: acidity; catalyst characterization (IR; molybdenum oxide/alumina-silica; UV-Via; XRD; acidity; catalyst characterization (IR; molybdenum oxide/alumina-silica; XRD; UV-Via
• ISSN: 0166-9834
• DOI: 10.1016/S0166-9834(00)83303-5

The structure of MoO 3/Al 2O 3-SiO 2 mixed oxide catalysts was studied by XRD, IR and UV-Vis spectroscopy. The nature of the Mo-O species formed depends on the composition of the amorphous Al 2O 3-SiO 2 and is controlled by the inhomogeneity of the Al 2O 3-SiO 2 carrier and the strong fixation of the molybdena on the separate alumina phase. The molybdenum is preferentially bound in the form of polymolybdates in the case of alumina-rich samples and as heteropolymolybdates or Al 2(MoO 4) 3 in the case of silica-rich samples. The formation of heteropolymolybdates or Al2 (MoO 4) 3 is due to the thermal instability of the amorphous Al 2O 3-SiO 2. Introduction of molybdena generates new Brønsted acid sites on the surface of alumina-rich Al 2O 3-SiO 2 supports. On the other hand no changes in Brønsted acidity induced by the molybdena has been found in catalysts with medium and low amounts of alumina.