Oxidation of ethanol to acetaldehyde over Na-promoted vanadium oxide catalysts

Sodium-promoted vanadium oxide catalysts supported on MCM-41 and TiO2 (anatase) were investigated for the partial oxidation of ethanol to acetaldehyde. The catalysts were prepared by incipient wetness impregnation with a vanadium oxide content of 6 wt.%. The experimental characterization was performed by X-ray diffraction (XRD), N-2 adsorption, temperature-programmed reduction (TPR), and diffuse reflectance UV-vis. Temperature-programmed oxidation (TPO) was also used to identify carbon deposits on the spent catalysts. The presence of sodium plays a strong role in the dispersion and reducibility of the vanadium species as detected by TPR analysis and optical absorption spectroscopy. While sodium addition increases the dispersion of the VOx species, its presence also decreases their reducibility. Additionally, TPO of the spent catalysts revealed that an increase in the Na loading decreases the carbon deposition during reaction. In the case of the catalysts supported on MCM-41, these modifications were mirrored by a change in the activity and selectivity to acetaldehyde. Additionally, on the VOx/TiO2 catalysts the catalytic activity decreased with increasing sodium content in the catalyst. A model in which sodium affects dispersion, reducibility and also acidity of the supported-vanadia species is proposed to explain all these observations. (c) 2007 Elsevier B.V. All rights reserved.