Structural Characterization and Oxidehydrogenation Activity of CeO₂/Al₂O₃and V₂O₅/CeO₂/Al₂O₃Catalysts

Abstract

Structural characterization and oxidative dehydrogenation activity of CeO2/Al2O3 and V2O5/CeO2/Al2O3 catalysts for ethylbenzene (EB) to styrene were investigated systematically. The CeO2/Al2O3 catalyst was prepared by a deposition precipitation method, and a theoretical monolayer equivalent of 10 wt % V2O5 was dispersed over its surface by a wet impregnation method to obtain the V2O5/CeO2/Al2O3 catalyst. To understand thermal and textural stability, the synthesized catalysts were subjected to calcination at various temperatures (773−1073 K). Physicochemical characterization was performed using X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis, and BET surface area techniques. The XRD and RS results suggested that the CeO2/Al2O3 sample is thermally quite stable up to 1073 K and that the ceria exists in the form of an over layer on the surface of the alumina support. In the case of the V2O5/CeO2/Al2O3 sample, no crystalline V2O5 was observed from XRD results, indicating a highly dispersed form of vanadium oxide on the CeO2/Al2O3 carrier when calcined at 773 K. The XPS peak shapes and the corresponding electron binding energies indicate that the dispersed vanadium oxide selectively interacts with the ceria portion of the CeO2/Al2O3 support and forms a CeVO4 compound at higher calcination temperatures. Formation of CeVO4 is also established from XRD and RS measurements. Both CeO2/Al2O3 and V2O5/CeO2/Al2O3 samples were tested for oxidative dehydrogenation of EB to styrene by using dry air as an oxidant. The V2O5/CeO2/Al2O3 catalyst exhibits more conversion and selectivity than CeO2/Al2O3. The time-on-stream experiments further reveal that the V2O5/CeO2/Al2O3 catalyst exhibits stable activity and selectivity without fast deactivation.