Preparation of USY zeolite [formula omitted] supported catalysts from V(AcAc) 3 and NH 4VO 3. Catalytic properties for the dehydrogenation of n-butane in oxygen-free atmosphere

Abstract

The preparation of different samples of vanadia supported on ultrastable zeolite ( VO x /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 methods were employed for preparing VO x /USY samples: an organic route using V(AcAc) 3 and an inorganic route using NH 4VO 3. The characterization of the samples was performed with XRD, TPR, NH 3-TPD, and N 2 isotherms. From these results it is concluded that when VO x 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 V 2O 5 is formed on the USY surface. On the other hand, VO x /USY prepared from the organic precursor shows no destruction of the USY structure. In addition, highly dispersed VO x 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 NH 4VO 3 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 VO x /USY surface.