Influence of metal oxide modification of alumina on the dispersion and activity of vanadia catalysts

  • Lakshmi L
  • Alyea E
  • Srinivas S
 et al. 
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Abstract

Alumina was modified with 10 wt % MOx (MOx = TiO2, ZrO2, La2O3, or MgO) prior to its impregnation with 12 wt % vanadia. The catalysts VTiAl, VZrAl, VLaAl, and VMgAl were characterized by X-ray diffraction (XRD), electron spin resonance (ESR), FT-Raman spectroscopy, 51V solid state nuclear magnetic resonance (51V NMR), and oxygen chemisorption. The activities of the catalysts were determined by methanol partial oxidation and their acid?base properties were evaluated for the decomposition of 2-propanol. XRD and FT-Raman spectroscopy indicated the formation of bulk TiO2 and ZrO2 on the titania and zirconia modified alumina. 51V solid state NMR results suggest the presence of both octahedrally and tertrahedrally coordinated vanadia species in the catalysts VTiAl, VZrAl, and VAl and the presence of tetrahedrally coordinated vanadia species in the catalysts VLaAl and VMgAl. ESR spectra recorded at ambient temperature showed the presence of V4+ ions having axial symmetry. Oxygen chemisorption results indicated an enhanced number of reducible vanadia sites, i.e., redox sites in the modified catalysts. Metal oxide modification is found to influence significantly the surface coverage and the methanol partial oxidation activity of vanadia supported on alumina. With proper MOx modification enhanced reducibility of vanadia could be attained, which in turn makes the partial oxidation reaction of methanol more facile. Alumina was modified with 10 wt % MOx (MOx = TiO2, ZrO2, La2O3, or MgO) prior to its impregnation with 12 wt % vanadia. The catalysts VTiAl, VZrAl, VLaAl, and VMgAl were characterized by X-ray diffraction (XRD), electron spin resonance (ESR), FT-Raman spectroscopy, 51V solid state nuclear magnetic resonance (51V NMR), and oxygen chemisorption. The activities of the catalysts were determined by methanol partial oxidation and their acid?base properties were evaluated for the decomposition of 2-propanol. XRD and FT-Raman spectroscopy indicated the formation of bulk TiO2 and ZrO2 on the titania and zirconia modified alumina. 51V solid state NMR results suggest the presence of both octahedrally and tertrahedrally coordinated vanadia species in the catalysts VTiAl, VZrAl, and VAl and the presence of tetrahedrally coordinated vanadia species in the catalysts VLaAl and VMgAl. ESR spectra recorded at ambient temperature showed the presence of V4+ ions having axial symmetry. Oxygen chemisorption results indicated an enhanced number of reducible vanadia sites, i.e., redox sites in the modified catalysts. Metal oxide modification is found to influence significantly the surface coverage and the methanol partial oxidation activity of vanadia supported on alumina. With proper MOx modification enhanced reducibility of vanadia could be attained, which in turn makes the partial oxidation reaction of methanol more facile.

Author-supplied keywords

  • Modified alumina
  • Partial oxidation
  • Vanadia

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