Synthesis, characterization and activity studies of vanadia catalysts supported on sol-gel derived Al2O3-ZrO2 mixed oxide

A series of catalysts with vanadia contents varying between 4 and 18 wt% were prepared using sol-gel derived alumina-zirconia mixed oxide as a support. The catalysts were characterized employing V-51, H-1 solid-state MAS NMR, diffuse reflectance FT-IR and BET surface area measurements. The activities of the catalysts were tested for the partial oxidation of ethanol. 51V NMR studies indicated the presence of tetrahedral vanadate species at all the loadings studied except in the catalyst with a V2O5 loading of 18 wt.%, in which six coordinated vanadia species was observed. Upon outgassing: treatment of the calcined catalysts, a new tetrahedral species:was observed, indicating the presence of water molecules or hydroxyl groups in the coordination sphere of vanadium. The H-1 MAS NMR studies showed the peaks corresponding to hydroxyl groups of alumina and zirconia. With increase in vanadia loading there was a decrease in the intensity of the basic hydroxyl groups of alumina showing the preferential reaction of vanadia with these groups. The DRIFT studies of the catalysts indicated the vibrations corresponding to agglomerates of V2O5 only in the sample with highest V2O5 content. Ethanol partial oxidation studies of the catalysts showed acetaldehyde as the major product with traces of ether, acetic acid, ethyl acetate, COx, etc. (C) 2000 Elsevier Science B.V. All rights reserved.