Preparation, Solid-state Characteristics, and Catalytic Properties of Promoted Vanadium Phosphate Materials (original) (raw)

Nature of Vanadium Sites in V/α-Ti Phosphate Catalysts for the Oxidative Dehydrogenation of Ethane☆

Journal of Catalysis, 1999

The selective conversion of ethane into ethylene is currently being studied because of the economic impact of using natural gas and LPG's raw materials to produce chemicals and polymers (1). The available technology for the production of ethylene is the steam cracking of ethane, although it is a highly energy-intensive process. Several approaches to this problem have been considered, although ethane dehydrogenation (ODH) remains prominent. The principal reason for this lies in the fact that dehydrogenation in the presence of oxygen is thermodynamically favored and coking side reactions are minimized.

The chemistry of catalysts based on vanadium-phosphorus oxides

1984

Vanadium-phosphorus mixed oxides, catalysts for C4 oxidation to maleic anhydride, were prepared in organic medium and tested in n-butane and butene-1 selective oxidation. These catalysts were compared with those prepared in aqueous medium. Before calcination, the two methods of preparation gave rise to the same phase, but the catalysts prepared in oraanic medium were characterized by higher surface area and lower oxidability in air. The latter characteristic makes it possible to obtain the selective compound of vanadium(IV) B-phase, (after calcination in air), in the full 0.95-1.15 P:V ratio range without the phases of vanadium(V) obtained in the case of catalysts prepared in aqueous medium. Unlike catalysts prepared in aqueous medium, an excess of phosphorus with respect to the ratio 1.0 led to a decrease both in activity and selectivity to maleic anhydride. The higher surface area of catalysts prepared in organic medium makes it possible to oxidize n-butane at lower temperatures than with catalysts prepared in aqueous medium.

Characterization and reactivity of Al2O3–ZrO2 supported vanadium oxide catalysts

Journal of Molecular Catalysis A: Chemical, 2006

Vanadium oxide catalysts with V 2 O 5 loadings ranging from 2.5 to 20 wt.% supported on Al 2 O 3 -ZrO 2 (1:1 wt.%) mixed oxide have been prepared by wet impregnation method. The calcined samples were characterized by X-ray diffraction (XRD), BET surface area, pulse oxygen chemisorption, electron spin resonance (ESR), temperature-programmed reduction (TPR) of H 2 , X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectroscopy (UVDRS). The catalytic properties have been evaluated for vapor phase ammoxidation of toluene to benzonitrile. Dispersion of vanadia was determined by the pulse oxygen chemisorption method at 643 K. Vanadia is found to be present in a highly dispersed state at lower loadings and dispersion decreases steadily with increase of vanadia loading. The ESR spectra obtained under ambient conditions shows the presence of V 4+ in tetrahedral symmetry. The TPR results show a single reduction peak corresponding to V 5+ →V 3+ . XPS results reveal that vanadium is present in a fully oxidized state (+5) in all the samples. The intensity ratio V 2p 3/2 /Al 2p 3/2 and V 2p 3/2 /Zr 3d 5/2 is found to increase with increase in vanadia loading up to 12.5 wt.% and levels off at higher vanadia loadings. The UV-vis diffuse reflectance spectra indicate the existence of isolated and clusterized tetrahedral (Td) V 5+ species in all catalysts. Ammoxidation activity increases with vanadia loading up to 12.5 wt.%, which corresponds to monolayer coverage and remains constant at higher vanadia loadings. The catalytic activity in ammoxidation of toluene to benzonitrile has been correlated to the oxygen chemisorption sites.

Reaction of methanol and n-propanol over hydrotalcite-like catalysts containing vanadium oxide

Applied Clay Science, 1998

Ž Vapour phase synthesis of isobutyric aldehyde from methanol and n-propanol molar ratio . 10:1 was carried out in a fixed bed reactor over calcined hydrotalcites and hydrotalcite-like compounds containing various amounts of vanadium oxide. V O was loaded by impregnation or 2 5 by decomposition of intercalated decavanadate ions. The influence of the MgrAl ratio, and the V O content as well as effect of some other reaction parameters was studied for both types of 2 5 catalysts. The mechanism of isobutyric aldehyde formation from n-propyl alcohol and methanol involves formation of metal enolates as intermediates. The catalysts were characterized by X-ray Ž . Ž . diffraction XRD , temperature-programmed reduction TPR , surface area and basicity measurements. q

Characterization and reactivity of vanadium oxide catalysts supported on niobia

Applied Catalysis A: General, 2003

A series of V 2 O 5 /Nb 2 O 5 catalysts with vanadia loading varying from 2 to 12 wt.% were prepared and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR), BET surface area and oxygen chemisorption at 640 K. The catalytic properties have been evaluated for vapor phase ammoxidation of 3-picoline to nicotinonitrile. XRD results suggest the formation of ␤-(Nb,V) 2 O 5 phase at higher loadings. TPR profiles showed two peaks: the low temperature peak is due to reduction of surface vanadia species and the high temperature peak is due to reduction of Nb 2 O 5 . XPS results reveal that both vanadia and niobia are present in fully oxidized state (5+) in all the samples. The intensity ratio V 2p 3/2 :Nb 3d 5/2 is found to increase with increase in vanadia loading up to 6 wt.% and to remain constant at higher vanadia loadings. The oxygen uptake increases with increase of vanadia loading on niobia, whereas the dispersion of vanadia decreases. The dispersion of vanadia measured by oxygen chemisorption method is in good agreement with the dispersion determined from XPS. The ammoxidation activity increases with vanadia loading up to 6 wt.%, which corresponds to monolayer coverage and remains constant at higher vanadia loadings. The catalytic properties during ammoxidation of 3-picoline are related to the oxygen chemisorption sites.