Atomic layer deposition and surface characterization of highly dispersed titania/silica-supported vanadia catalysts

The atomic layer deposition (ALD) method using surface-saturating gas-solid reactions was applied to modify a highly dispersed titania/silica support with submonolayer amounts of vanadia. The surface properties and acidity of the V2O5/TiO2/SiO2 materials were examined relatively to the corresponding silica and titania supported samples. The surface area, porosity and amorphous nature of the support were not affected by vanadia, which was present in the form of highly dispersed isolated species on titania/silica, as detected by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Microcalorimetry measurements showed that the vanadia species interacted with both the titania overlayer and the silica surface, confirming the observed V-O-Ti bonding Raman features. The surface reactivity towards ammonia was strongly enhanced by the modification, as probed by adsorption microcalorimetry and XPS. The superiority of the ALD method for the preparation of bilayered vanadia/titania/silica catalysts was demonstrated by examining for comparison a series of aqueous-phase impregnated catalysts. (C) 2002 Elsevier Science B.V. All rights reserved.