Reactivity Of Vanadium Oxide Catalysts Research Articles

Characterization and reactivity of vanadium oxide catalysts supported on niobia

A series of V 2O 5/Nb 2O 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 β-(Nb,V) 2O 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 2O 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.

Studies on Dispersion and Reactivity of Vanadium Oxide Catalysts Supported on Titania

Vanadium oxide catalysts with V2O5 loadings ranging from 2 to 12% w/w supported on various modifications of titania have been prepared by the wet impregnation method. The calcined samples were characterized by X-ray diffraction (XRD), electron spin resonance (ESR), oxygen chemisorption, temperature-programmed desorption (TPD) of ammonia, and surface area measurements. The catalytic properties were evaluated for ammoxidation of 3-picoline to nicotinonitrile. Dispersion of vanadia was determined by the oxygen chemisorption at 640 K and by the static method on the samples prereduced at the same temperature. Oxygen chemisorption results suggest that vanadium oxide disperses better on TiO2 (anatase) than it is supported on TiO2 (rutile) or TiO2 containing mixture of anatase and rutile. ESR spectra obtained under ambient conditions for the catalysts reduced at 640 K show the presence of V4+ ions in axial symmetry. The results of XRD and ESR substantiate the findings of oxygen chemisorption. Ammonia TPD results ...

Dispersion and reactivity of vanadium oxide catalysts supported on niobia

Vanadium oxide catalysts supported on niobia are found to be highly active for ammoxidation of 3-picoline and it is found that the catalytic properties are directly related to the dispersion of vanadia.

Structure and Reactivity of Vanadium Oxide Catalysts Supported on Anatase TiO2

A series of TiO2 (anatase) supported vanadia catalysts with V2O5 loadings ranging from 2 to 12% were characterized by temperature-programmed reduction (TPR), X-ray diffraction, electron spin resonance (ESR), and oxygen chemisorption studies. TPR profiles indicate the presence of a single peak for the reduction and suggest that the reducibility of vanadia depends on its loading on TiO2. Dispersion of vanadia was determined by the static oxygen chemisorption method at 640 K on the samples prereduced at the same temperature. At low vanadia loadings, i.e., below 6%, vanadium oxide is found to be present in a highly dispersed state. A comparison of dispersion of vanadia determined by low-temperature oxygen chemisorption (samples reduced at 773 K for 6 h and subsequent oxygen chemisorption at 195 K) with that determined at 640 K shows that the latter method provides a better measure of dispersion of vanadia. ESR spectra obtained under ambient conditions for the catalysts reduced at 640 K show the presence of V4...