Partial oxidation of ethanol over ZrO2-supported vanadium catalysts

Zirconia-supported vanadium catalysts were prepared by the wet impregnation of two different zirconia supports using ammonium metavanadate in aqueous hydrogen peroxide solution. The catalysts were characterized by N-2 physisorption, X-ray fluorescence analysis (XRF), X-ray diffraction (XRD) and Raman spectroscopy to determine their textural properties, chemical composition and the nature of vanadium species. The partial oxidation of ethanol to acetaldehyde was carried out in a fixed bed reactor at atmospheric pressure varying the weight-hourly space velocity and temperature in the range 1-4 h(-1) and 150-250 degrees C, respectively. In addition to acetaldehyde, a range of oxygenated and deoxygenated by-products was observed. Diethyl ether and ethyl acetate were detected in the reaction mixture with low and almost constant amount. These products are formed through a homogeneous reaction in the free volume of reactor or pre-heating zone irrespective of catalyst used. Vanadium species anchored on the zirconia surface are able to activate ethanol molecules already at 150 degrees C with the high selectivity to acetaldehyde. A comparison of vanadium speciation and catalytic results led to conclusion that oligomeric vanadium species and small oxide clusters have no deterioration effect on acetaldehyde selectivity.