Influence of the preparation procedure on the nature and environment of vanadium in VSiBEA zeolite: XRD, DR UV-vis, NMR, EPR and TPR studies - Sorbonne Université Access content directly
Journal Articles Microporous and Mesoporous Materials Year : 2012

Influence of the preparation procedure on the nature and environment of vanadium in VSiBEA zeolite: XRD, DR UV-vis, NMR, EPR and TPR studies

Abstract

Two series of VxSiBEA(I) and VxSiBEA(II) zeolites have been prepared by a two-steps postsynthesis method which consists, in the first step, in the dealumination of TEABEA zeolite by two different procedures to obtain SiBEA(I) and SiBEA(II) zeolites and then, in the second step, in contacting the obtained zeolites with an aqueous NH4VO3 solution at pH 2.7. Because the NH4VO3 solution at pH 2.7 predominantly contains mononuclear VO2+ ions, vanadium can be incorporated into SiBEA(I) and SiBEA(II) as framework pseudo-tetrahedral non hydroxylated (SiO)3V(V)double bond; length as m-dashO and hydroxylated (SiO)2(OH)V(V)double bond; length as m-dashO species by reaction with silanol groups of vacant T-atom sites. Combined use of FTIR, DR UV-vis, 51V NMR, EPR and TPR allows to determine the oxidation state, nature and environment of vanadium in as prepared, calcined, rehydrated, activated and reduced VxSiBEA(I) and VxSiBEA(II) samples. It is shown that the procedure of dealumination has the effect on the properties of the silanol groups of vacant T-atom sites in SiBEA(I) and SiBEA(II) and on the nature and environment of V species in as prepared VxSiBEA(I) and VxSiBEA(II). As evidenced by DR UV-vis and 51V MAS NMR in VxSiBEA(II), vanadium is present only as pseudo-tetrahedral V(V) species, and in contrast in VxSiBEA(I) as pseudo-tetrahedral and octahedral V(V) species. The oxidation state of framework tetrahedral vanadium in VxSiBEA(I) and VxSiBEA(II) easily change upon calcination in oxygen, outgassing at 773 K and reducing with hydrogen at high temperature (873 K), as shown by EPR. The presence of Brønsted and Lewis acidic centres are evidenced in VxSiBEA(II) by FTIR adsorption investigations of pyridine and CO used as probe molecules.

Keywords

Domains

Catalysis

Dates and versions

hal-00744705 , version 1 (23-10-2012)

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Cite

Rafal Baran, Yannick Millot, Thomas Onfroy, Frédéric Averseng, Jean-Marc Krafft, et al.. Influence of the preparation procedure on the nature and environment of vanadium in VSiBEA zeolite: XRD, DR UV-vis, NMR, EPR and TPR studies. Microporous and Mesoporous Materials, 2012, 161, pp.179-186. ⟨10.1016/j.micromeso.2012.05.023⟩. ⟨hal-00744705⟩
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