Preparation of USY zeolite VOx supported catalysts from V(AcAc)3 and NH4VO3.: Catalytic properties for the dehydrogenation of n-butane in oxygen-free atmosphere

The preparation of different samples of vanadia supported on ultrastable zeolite (VOx/USY) is discussed. The samples were prepared in order to obtain highly dispersed V-species, avoiding the formation of crystalline vanadia and the destruction of the zeolite framework. Two VOx/USY samples: an organic route Using V(AcAC)(3) and an inorganic route Using NH4VO3. The characterization of the samples was performed with XRD, TPR, NH3-TPD, and N-2 isotherms. From these results it is concluded that when VOx is supported on the surface of USY from acidic aqueous solution of ammonium metavanadate. the destruction of the zeolite framework is accomplished. For higher pH values in the impregnating solution, undesired V2O5 is formed oil the USY Surface. Oil the other hand, VOx/USY prepared fro, the organic precursor shows no destruction of the USY structure. In addition. highly dispersed VOx are formed, though for relatively high V loadings (6%) an obstruction of the zeolite windows takes place. The samples are tested as catalysts for gas phase dehydrogenation of n-butane to olefins. The catalysts prepared from NH4VO3 are almost inactive for the reaction. On the other hand, both samples prepared from V(AcAc)(3) present initial conversion levels in the 8-12% range. However, the selectivity depends on the V loading, the catalysts with 6% loading being the most selective (75%). The catalytic patterns of the samples (activity and selectivity) are in agreement with the physicochemical features of the VOx/USY surface. (c) 2005 Elsevier Inc. All rights reserved.