The dehydrogenation of ethylbenzene with CO2 over V2O5/CexZr1-xO2 prepared with different methods

The high-surface-area CexZr1-xO2 composite oxides with various compositions were prepared with modified hydrothermal and sol-gel methods, respectively. Different amounts of vanadia were loaded via an incipient wetness technique for the preparation of the V2O5/CexZr1-xO2. The prepared samples were subjected to the dehydrogenation of ethylbenzene (EB) in the presence of CO2 in a fixed-bed reactor under the conditions of T = 823 K, P = 1 atm, and CO2/BE molar ratio = 20. The hydrothermal CexZr1-xO2 loaded with 6 wt.% V2O5 showed obviously higher EB conversion than the 6 wt.% V2O5/CexZr1-xO2 (sol-gel) although similar styrene selectivity was obtained. Moreover, the V2O5 loadings and the Ce/Zr ratios had clear influence on both the activity and the stability of the catalyst. Irrespective of the preparation methods and Ce/Zr ratios, XRD results indicate that nanocrystalline CexZr1-xO2 solid solution was exclusively formed. Independent of the Ce/Zr ratios, the CexZr1-xO2 prepared with hydrothermal method was composed of pure cubic phase while mixed phases were observed for the sol-gel samples as revealed from Raman results. With increasing vanadia loadings from 3 to 15 wt.%, different forms of vanadium species, such as vanadates and crystalline V2O5, were observed from Raman spectra. Irrespective of the V2O5 loadings, a single-step reduction of the supported V2O5 was revealed from the TPR patterns. Based on these and the TGA/DSC analysis of the used catalysts, the experimental results were extensively discussed and tentatively explained. (C) 2010 Elsevier B.V. All rights reserved.