Effect of potassium addition to the TiO2 support on the structure of V2O5/TiO2 and its catalytic properties in the oxidative dehydrogenation of propane

DOI: 10.1039/ft9969201609

Source and publish data:

Journal of the Chemical Society - Faraday Transactions p. 1609 - 1617 (1996)

Update date:2022-08-12

Topics:

Authors:

Courcot, Dominique

Grzybowska, Barbara

Barbaux, Yolande

Rigole, Monique

Ponchel, Anne

Guelton, Michel

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Article abstract of DOI:10.1039/ft9969201609

Vanadium oxide has been deposited by a grafting technique onto TiO₂ anatase, both pure and doped with potassium [(1.2 and 2.5) atoms nm^-2]. The V content varied between 0.1 and 20 atoms nm^-2 [0.01-2 V₂O5 monolayers (ML)]. The prepared samples were characterized by X-ray photoelectron spectroscopy (XPS), ⁵¹V magic-angle spinning (MAS) NMR and a surface potential (SP) technique and tested as catalysts in the oxidative dehydrogenation (ODH) of propane and propan-2-ol decomposition, a probe reaction for acid-base properties. From the XPS and SP data it has been inferred that VO_x are located beside the K centres on the bare surface of TiO₂ with the lower K content sample, whereas they cover the K-doped fraction of the surface for the sample with higher K content. Monomeric and polymeric VO_x species and V₂O₅ were detected by ⁵¹V NMR on pure and K-doped catalysts. For the K-doped samples the polymeric species were observed only at high V content and new tetrahedral VO_x species and traces of KVO₃ appeared. It has been found that the presence of K on the TiO₂ surface leads to (a) a decrease in the reducibility of the vanadia phase at low V content; (b) a decrease in the surface potential (electronic work function); (c) a decrease in acidity and increase in basicity and (d) a decrease in the total activity for ODH of propane. The pattern of the activity and selectivity changes with the total V content depends on the amount of K on the support surface: with K < 1 ML, the maximum activity and selectivity is observed at a vanadium content corresponding to ca. 40% of a V₂O₅ ML. At higher K content, higher amounts of vanadium (> 1 ML) are required to obtain the same catalytic performance. Polymeric [VO_x] species seem to be more active and selective in the ODH of propane than monomeric species or bulk V₂O₅.