Synthesis and characterization of alumina-supported vanadium oxide catalysts prepared by the molecular designed dispersion of VO(acac)2 complexes

Abstract

Alumina-supported vanadium oxide catalysts have been prepared by the molecular designed dispersion method, using the vanadyl acetylacetonate complex (VO(acac)₂). The complex has been adsorbed on the support from solution, followed by thermal conversion into the corresponding supported vanadium oxide catalyst. The formation of the VO(acac)₂–support material has been studied by both spectroscopic (FTIR, FT-Raman, ESR, UV–VIS–DRS; DRS: diffuse reflectance spectroscopy) and chemical methods. The present study reveals that VO(acac)₂ complexes react preferentially with the hydroxy groups of the alumina, and only to a limited extent with the coordinatively unsaturated Al³⁺ sites. In addition, the deposition of the VO(acac)₂ complex on the alumina surface yields different supported vanadium configurations as a function of the surface loading, due to both ligand exchange and hydrogen bond interactions. The thermal conversion of the adsorbed VO(acac)₂ complexes into the supported vanadium oxide catalyst has been studied by TGA, GC-FTIR and in situ IR, which provides additional information on the VO(acac)₂–support interaction. Characterization of these supported vanadium oxide catalysts by FTIR, FT-Raman and UV–VIS–DRS reveals the formation of highly dispersed VO_x functionalities.