Untersuchungen an katalytisch aktiven Oberflächenverbindungen. XIII. Struktur und katalytische Eigenschaften von Molybdän-oxid/SiO2-Katalysatoren |
| |
Authors: | M Selenina R Fricke W Hanke K-H Schnabel G
hlmann |
| |
Institution: | M. Selenina,R. Fricke,W. Hanke,K.-H. Schnabel,G. Öhlmann |
| |
Abstract: | Studies on Catalytically Active Surface Compounds. XIII. Structure and Catalytic Properties of Molybdenum Oxide/SiO2 Catalysts The catalytic properties of Mo oxide/SiO2 catalysts in the selective oxidation of methanol to formaldehyde are described. It is shown that, independently on the preparation conditions, all catalysts showed relative high activity and selectivity values which were however, not constant during the reaction time. The high initial activity could be stabilized to a limited extent both by prereduction with methanol (but not with hydrogen) and by decreasing the oxygen concentration of the reaction gas. ESR measurements showed that in dependence on the means of reduction (methanol or hydrogen) two different coordinated Mo5+ ions were formed. Evidence was given by IR spectroscopy that prereduction in methanol caused the formation of methoxy groups stabilizing catalytically active Mo5+ ions. UV-Vis, ESCA, and electron microscopic measurements showed however, that further aggregation and formation of microcrystallites of MoO3 took place during the catalytic reaction which caused the observed decrease of the activity. |
| |
Keywords: | |
|
|