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PREPARATION, CHARACTERIZATION AND ACTIVITY OF AL2O3-SUPPORTED V2O5 CATALYSTS
Citation:
Reddy**, E P. AND R S. Varma*. PREPARATION, CHARACTERIZATION AND ACTIVITY OF AL2O3-SUPPORTED V2O5 CATALYSTS. E. Iglesia (ed.), JOURNAL OF CATALYSIS. Elsevier Online, New York, NY, 221(1):93-101, (2003).
Description:
A series of activated alumina supported vanadium oxide catalysts with various V2O5 loadings ranging from 5 to 25 wt% has been prepared by wet impregnation technique. A combination of various physico-chemical techniques such as BET surface areas, oxygen chemisorption, X-ray diffraction (XRD), temperature programmed reduction (TPR), thermal gravimetric analysis (TGA) and Fourier transform infrared (FTIR) was used to characterize the chemical environment of vanadium on the alumina surface. XRD and FTIR results suggest that vanadium oxide exists in a highly dispersed state below 15 wt% V2O5 loading and in microcrystalline phase above this loading level. TPR profiles of V2O5/Al2O3 catalysts exhibit only a single peak at low temperature up to 15 wt% V2O5. It is suggested that the low temperature reduction peak is due to the reduction of surface vanadia, which has been ascribed to the tetrahedral coordination geometry of the V ions therein. The TPR profiles of V2O5/Al2O3 catalysts indicate that at loading lower than 15% vanadia forms isolated surface vanadia species, while two dimensional structure and V2O5 crystallites become the prevailing species in highly loaded (> 15% V2O5) systems. Liquid phase oxidation of ethylbenzene to acetophenone has been employed as a chemical probe reaction to examine the catalytic activity. Ethylbenzene oxidation results reveal that 15%V2O5/Al2O3 is more active than higher vanadia loading catalysts.