Bulk and surface structures of V2O5/ZrO2 catalysts for n-butane oxidative dehydrogenation

Structure, Acidity, and Redox Aspects of VOx/ZrO2/SiO2 Catalysts for the n-Butane Oxidative Dehydrogenation

ZrOx/SiO2 and VOx/ZrOx/SiO2 catalysts (5 wt %–25 wt % Zr, 4 wt % V) were prepared by grafting zirconium and vanadium alkoxides on Aerosil 380. All samples were characterized by temperature programmed reduction, N2 physisorption, X-ray diffraction, Raman spectroscopy, and ammonia adsorption microcalorimetry. Tetragonal ZrO2 and zircon (ZrSiO4) were present at 25 wt % Zr, but only amorphous zirconia overlayer existed for lower loadings. At lower Zr loadings (5 wt %–10 wt % Zr), exposed silica surface leads to V2O5 crystallites and isolated VO4 species, although V reducibility behavior changes, from being similar to VOx/SiO2 (5 wt % Zr) to showing VOx/ZrO2 behavior at 10 wt % Zr, and a diminished total amount of reducible V. Highly acidic ZrO2 sites are covered by the vanadium grafting, forming weaker sites (60–100 kJ/mol NH3 adsorption strength). Catalytic conversion and selectivity for the oxidative dehydrogenation of n-butane (673 K, n-C4/O2 = 2.2) over VOx/ZrOx/SiO2 show that 1,3-butadiene is favored over cis-2-butene and trans-2-butene, although there is some selectivity to the 2-butenes when VOx/ZrO2 behavior is evident. At low Zr loadings, butadiene formed during reaction acts as the diene species in a Diels–Alder reaction and gives rise to a cyclic compound that undergoes further dehydrogenation to produce benzaldehyde.

Morphology-Oriented ZrO2-Supported Vanadium Oxide for the NH3-SCR Process: Importance of Structural and Textural Properties

ZrO₂ supports, with diverse morphologies (hollow sphere, star, rod, mesoporous), were produced using hydrothermal and evaporation-induced self-assembly methods. Zirconia-supported vanadium oxide catalysts were prepared by wet impregnation and used for the low-temperature selective catalytic reduction (SCR) of NO with ammonia. Characterization of catalysts includes N₂ physisorption, elementary analysis, X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction by H₂, and temperature-programmed desorption of NH₃. Significant differences in terms of activity are measured. 3 wt % V₂O₅ supported on mesoporous ZrO₂ (V/MZ) presents excellent N₂ yields (>90%, in the 200-400 °C interval), with a wide operating temperature window (NO conversion > 95%, in the 225-425 °C interval), and less interesting performances were obtained when vanadium oxide is supported over stars, hollow spheres, and rods. Surface characterization showed a content of tetravalent vanadium ion, when supported, decreasing in the order of mesoporous > hollow sphere > star > rod. This order is in perfect agreement with the order of performance of the catalyst in the NH₃-SCR reaction. The impact of tetravalent ion's presence on the surface is confirmed by diffuse reflectance infrared Fourier transform spectroscopy analysis, Brønsted acid sites generated on the surface, and the V⁴⁺-OH species involved in the reaction. The production of more important nitrite species over the tetragonal supported vanadium oxide catalyst could be another reason for the excellent NH₃-SCR performance displayed by the V/MZ catalyst. When supported over monoclinic zirconia, like vanadium oxide over star-type morphology, the adsorbed NH₃ species (NH₄⁺ and coordinated NH₃) reacted with NO _x adsorption species (nitrate) to form ammonium nitrate. Ammonium nitrate can be decomposed to N₂ and N₂O (or NO₂). Thus, NO conversion curves and N₂ yield curves over tetragonal zirconia (MZ) at lower temperature were ahead of those over V/star ZrO₂ because of the higher V⁴⁺ surface content and more active B acid sites associated with an easy formation of the nitrito intermediate.

VRK, Y. W. S, P. S. SP, N. L. One-step selective synthesis of 2-chlorobenzonitrile from 2-chlorotoluene via ammoxidation

Isolated and polymeric vanadia formulate V₂O₅/Al₂O₃ catalysts selective for the synthesis of 2-chlorobenzonitrile from 2-chlorotoluene in a single step through ammoxidation.

Oxidative dehydrogenation of 1-butene over vanadium modified bismuth molybdate catalyst: an insight into mechanism

The effect of vanadium addition on the performance of bismuth molybdate catalysts has been discussed. The mechanism of oxygen mobility on the prepared catalysts is proposed.