Flame-made vs. wet-impregnated vanadia/titania in the total oxidation of chlorobenzene: Possible role of VO x species

Abstract

Vanadia/titania particles with a specific surface area (SSA) around 50 m 2 g −1 and a V 2O 5 content up to 30 wt.% (corresponding to a V surface density up to 33 V nm −2) were prepared by flame spray pyrolysis as well as by classic wet-impregnation. The catalysts were characterized by nitrogen adsorption, X-ray diffraction, temperature programmed reduction, Raman spectroscopy, X-ray photoelectron spectroscopy and tested in the total oxidation of chlorobenzene. Depending on vanadia content, monomeric, polymeric and crystalline vanadia species were formed. The dispersion of the VO x species was in general higher for flame-made catalysts. While the classic wet-impregnated catalysts already showed crystalline V 2O 5 when the V surface density reaches 8 V nm −2, the flame-made ones exhibited only amorphous VO x species up to 16 V nm −2. The activity of flame-made and wet-impregnated catalysts increased with increasing V 2O 5 loading and therefore depended on the VO x species structure: catalysts exceeding a V surface density of 8 V nm −2 containing high amounts of amorphous polymeric and/or crystalline VO x species showed significantly higher activity than catalysts with lower V surface density. Wet-impregnated catalysts with numerous V–O–V bonds as involved in polymeric and crystalline VO x species showed superior activity than FSP-made ones of similar composition. This contribution proposes a discussion aiming at understanding the role played by the different types of VO x species in the total oxidation of volatile organic compounds on the example of chlorobenzene.