Structure and catalytic properties of molybdenum oxide catalysts supported on zirconia

MoO3/ZrO2 catalysts with different MoO3 loadings (2–12 wt%) were prepared by the wet impregnation method. These catalysts were characterized by various techniques, such as X-ray diffraction (XRD), temperature-programmed reduction (TPR), laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption of NH3 and the catalytic properties were evaluated for vapor-phase ammoxidation of toluene to benzonitrile. XRD patterns show the presence of crystalline MoO3 peaks above 6.6 wt% MoO3, which corresponds to the theoretical monolayer loading of MoO3 on the zirconia used in the present study. The TPR suggests that reduction of the catalysts occurs in two stages and indicates that the reducibility of the catalysts increases with increase in MoO3 loading up to 6.6 wt%. The acidity of the catalysts was also found to increase up to 6.6 wt% of molybdena loading and it does not increase much at higher loadings. Raman results show that the surface molybdate species are present in low-loading samples, while crystalline MoO3 bands are observed from 9 wt% of MoO3 and above loadings. XPS spectra showed that molybdenum was present at Mo6- on all fresh samples. The Mo/Zr atomic ratio shows that the dispersion of molybdena is high below 6.6 wt% MoO3 and dispersion decreases at higher molybdena loadings. The catalytic activity of the catalysts during ammoxidation of toluene was found to increase with loading up to 6.6 wt% and did not change appreciably beyond this loading

Characterization and reactivity of vanadium oxide catalysts supported on niobia

A series of V2O5/Nb2O5 catalysts with vanadia loading varying from 2 to 12 wt.% were prepd. and characterized by X-ray diffraction (XRD), XPS, temp. programmed redn. (TPR), BET surface area and oxygen chemisorption at 640 K. The catalytic properties have been evaluated for vapor phase ammoxidn. of 3-picoline to nicotinonitrile. XRD results suggest the formation of b-(Nb,V)2O5 phase at higher loadings. TPR profiles showed two peaks: the low temp. peak is due to redn. of surface vanadia species and the high temp. peak is due to redn. of Nb2O5. XPS results reveal that both vanadia and niobia are present in fully oxidized state (5+) in all the samples. The intensity ratio V 2p3/2:Nb 3d5/2 is found to increase with increase in vanadia loading up to 6 wt.% and to remain const. 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 detd. from XPS. The ammoxidn. activity increases with vanadia loading up to 6 wt.%, which corresponds to monolayer coverage and remains const. at higher vanadia loadings. The catalytic properties during ammoxidn. of 3-picoline are related to the oxygen chemisorption sites. [on SciFinder (R)