Improvement of catalytic functions of binary V-Sb oxide catalysts for oxidative conversion of isobutane to isobutene

Dehydrogenation of isobutane in the presence of oxygen-industrially prospective process for isobutene production-has been studied over vanadium-antimony oxide catalysts. Their catalytic behaviour was compared with the sample characterisation data by specific surface area (SSA), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Substantial improvement of the catalytic performance has been achieved as a result of proper spreading of active V-containing component onto an appropriate support. Optimisation of the composition and loading of the active component, the chemical nature and morphology of support material, as well as the preparation procedure allowed to further improve the yield of isobutene. Microspheric gamma-alumina with moderate SSA and large average pore diameter was found to be the best support for the efficient catalyst. The loading of vanadia corresponding to 1-1.5 formal monolayer coverage and doping with antimony (V-to-Sb atomic ratio 8.8) were found to be optimal. The use of "citrate" preparation technique showed an advantage in comparison with ordinary impregnation method, giving the catalyst with well dispersed (amorphous) and homogeneously distributed supported V-Sb-O-component. The optimised catalyst demonstrated improved stability, high activity and olefin selectivity (70% at 36% conversion), producing yields of isobutene (up to 26% per pass) among the best reported in the literature. (C) 2003 Elsevier Science B.V. All rights reserved

Oxidative conversion of isobutane to isobutene over V-Sb-Ni oxide catalysts

Insertion of proper amounts of nickel oxide into alumina-supported V-Sb oxide catalyst for the oxidative dehydrogenation of isobutane substantially increases isobutane conversion (from 36 to 42-44%) at selectivity to isobutene similar to70%. Fresh and used catalysts (including reference bulk V-Sb-O and V-Sb-Ni-O systems) were characterised by BET, XRD, XPS and H-2-TPR. Formation of new phase of nickel vanadate NiV2O6 at the expense of free VOx-phase leads to more reducible catalyst with increased amounts of mobile lattice oxygen. The facile redox cycle of vanadium species is considered to improve the catalyst activity. (C) 2003 Elsevier Science B.V. All rights reserved

Physico-chemical properties of V-Sb-oxide systems and their catalytic behaviour in oxidative dehydrogenation of light paraffins

Catalysts prepared as bulk VSb0.1Ox and supported V2O5/Al2O3. V2O5-Sb2O3/Al2O3 and Sb2O3/Al2O3 (containing 0.5, 1 or 2 theoretical monolayers of V2O5 or Sb2O3) were tested in the oxidative dehydrogenation of iso-butane at 550 degrees C in i-C4H10:O-2 :He=20:10:70 gas mixture. Fresh and used catalysts were characterised by BET, XRD and XPS, Reactivity and thermochemistry of active oxygen taking part in the redox cycle with ethane and hydrogene were studied using in situ differential scanning calorimetry. Temperature-programmed desorption of O-2 in He Row was also investigated and in situ DRIFT was applied to investigate surface species of the catalysts in flows of i-C4H10, O-2 and i-C4H10/O-2 mixture. Supported VSbyOx catalysts are more active and selective than bulk one. V-only supported catalysts display a high efficiency due to the high reactivity of VOX-species. In bulk catalyst, the surface is enriched with antimony. In supported samples, the surfaces V/Sb are close to the calculated ones. In the presence of antimony, the amount of active oxygen species and their reactivity in redox transformation is improved. The rates of vanadium reduction and reoxidation are also higher. Compared to V-only catalysts, supported V-Sb-catalysts display a lower coking activity and higher on-stream stability. (C) 2000 Published by Elsevier Science B.V