Bulk and Surface Structures of V₂O₅/ZrO₂ Systems and Their Relevance for o-Xylene Oxidation

Abstract

Zirconia-supported vanadium oxide systems, with V2O5 loadings ranging from V/Zr ) 0.033-0.270 atom ratios (0.2-2 monolayers), were prepared by impregnation of a porous ZrO2 substrate with ammonium metavanadate solutions. The surface structures of air-calcined samples were elucidated by Raman and X-ray photoelectron spectroscopic techniques and thermal desorption methods. Some insight into how the bulk structures of these materials developed upon thermal treatment was derived from the X-ray diffraction patterns and temperature-programmed reduction. At low V content, surface-dispersed vanadium oxide species were formed, which produced the transformation of the ZrO2 support from the tetragonal phase into the monoclinic one. At higher vanadium oxide contents, a solid-state reaction between V2O5 and ZrO2 occurred, with subsequent formation of the ZrV2O7 phase, this being the major V-containing phase. The reactivity of these surface structures was examined by looking at their performance for the oxidation of o-xylene to phthalic anhydride. Activity tests indicated that surface vanadium oxide species were more active for the oxidation of o-xylene but had a lower selectivity to phthalic anhydride.

Vanadium Supported on Alumina and/or Zirconia Catalysts for the Selective Transformation of Ethane and Methanol

“…Figure 2 presents the Raman spectra of supported vanadium oxide catalysts. In the case of Al 2 O 3 -supported catalysts (Figure 2a), all spectra show the presence of characteristics bands related to V 2 O 5 , i.e., 994, 702, 697, 527, 404, 284, and 146 cm −1 [50,51]. However, a broad band is also observed at ca.…”

“…Raman spectrum of pure ZrO 2 shows the presence of bands at 175, 190, and 477 cm −1 (related to m-ZrO 2 ) and bands at 263, 330, 472, 552, and 640 cm −1 (related to t-ZrO 2 ) [50]. These results are in good agreement to those previously reported for V 2 O 5 /ZrO 2 catalysts [50,54] in which the Raman spectrum of the supported 4% V 2 O 5 /ZrO 2 catalyst (with 8.1 V at./nm 2 ) contains bands from the dehydrated surface VO 4 species at 1035 and~935 cm −1 arising from the terminal V=O and bridging V-O-Zr bonds, respectively, as well as the presence of band at 860 cm −1 assigned to V-O-V vibrations in polyvanadate structures [52]. The Raman features at~630, 552,~528,~470,~375, and~330 cm −1 were related to crystalline monoclinic ZrO 2 support [50].…”

“…In the case of materials with Al/(Al + Zr) atomic ratios of 0.75 or 0.25 (i.e., BC and CC supports, respectively), new broad reflections are also observed at 2θ = 30.16 • and 50.65 • (their intensities increasing when increasing the Zr-content), which indicate the appearance of ZrO 2 crystallites with tetragonal symmetry. However, zirconia support (DC) is a mixture of monoclinic m-ZrO 2 (JCPDS file: 37-1484) and tetragonal t-ZrO 2 (JCPDS file: 27-997) phases [49,50]. In ZrO 2 -supported vanadium oxide catalysts (DC-series), it can be seen the presence of both monoclinic and tetragonal ZrO 2 and V 2 O 5 crystallites in the sample with highest V-loading, i.e., 8DC sample ( Figure 1d).…”

“…In ZrO 2 -supported vanadium oxide catalysts (DC-series), it can be seen the presence of both monoclinic and tetragonal ZrO 2 and V 2 O 5 crystallites in the sample with highest V-loading, i.e., 8DC sample ( Figure 1d). Moreover, the presence of mixed Zr-V oxides, as ZrV 2 O 7 (JCPDS file: 16-0422), cannot be ruled out in the case of sample 8DC [50,52].…”

Low temperature oxidation of o-xylene with hydrogen peroxide in the presence of vanadium xerogels

“…В качестве катализатора используется оксид ванадия (V) на носителе (SiO 2 , Al 2 O 3 , TiO 2 и ZrO 2 ) или смешанные ванадий-калий-сульфатносиликагелевые системы [5][6][7]. Выход фталевого ангидрида составляет 75-80%.…”