Vanadium oxide monolayer catalysts. 3. A Raman spectroscopic and temperature-programmed reduction study of monolayer and crystal-type vanadia on various supports

Abstract

Vanadium oxide monolayer catalysts. 3. A Raman spectroscopic and temperature-programmed reduction study of monolayer and crystal-type vanadia on various supports Roozeboom, F.; Mittelmeijer-Hazeleger, M.C.; Moulijn, J.A.; Medema, J.; de Beer, V.H.J.; Gellings, P.J. Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Link to publication• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Vanadium(V) oxide supported on 7-A1203, GO2, Cr2O3, Si02, Ti02, and Zr02 was studied by X-ray fluorescence, by X-ray diffraction, and especially by the combination of Raman spectroscopy and temperature-programmed reduction (TPR) for qualitative and quantitative structural analysis, respectively. Catalysts were prepared via ion-exchange and wet-impregnation methods. The V contents ranged from -1 to 40 wt % V. At low surface concentrations only surface vanadate phases of two-dimensional character are observed for all carriers. According to Raman and TPR data the structure of these surface vanadate species is independent of the preparation technique. At medium and high surface concentrations, the webimpregnated samples already contain crystalline V20b At equal surface concentrations the ion-exchanged catalysts contain no V205 crystallites. An exception is Si02 on which also crystalline V206 is formed in both preparation techniques. Monolayer stability toward thermal treatment decreases in the order AZO3 > Ti02 > Ce02, whereas on heating ion-exchanged V/Si02 the crystalline V206 spreads out over the silica surface. The reducibilities of the ion-exchanged catalyats, as measured by TPR, can be used as a measure for the contact interaction between vanadia and the carrier oxides. At temperatures of 500-800 K, this interaction ranges fr...

Study of the Surface Structure of V2O5/γ-Al2O3 Catalysts by LEIS

“…In the next regime (7-11 wt<>A,) the experiments show shielding of V atoms by additional V species without affecting the Al or 0 signal. The additional V atoms have an octahedral environment [20,21], which is consistent with the growth of a multilayered structure or lamellas as is shown in tigure 5. 7.c.…”

“…Laser Raman spectroscopie experiments by Roozeboom et al [19,20] showed that three different species may be present on the catalyst: vanadate tetrahedra, two-dimensional polymerie octahedral clusters and at higher of the vanadium oxide supported on y-alumina (9.8 wt%) have been given by Bergeret et al [22] using RED (radial electron distribution). These results indicate that the structure of the supported vanadium oxide is different trom bulk vanadium pentoxide ( fig.…”

The mechanism for the controlled synthesis of highly dispersed vanadia supported on silica SBA-15

“…To understand the correlation between structural and catalytic properties of dispersed vanadia, various techniques including infrared [16-18a,18b], Raman [19][20][21][22][23], UV-visible [16,17,20,24,25], solid-state 51 V NMR [21], and X-ray absorption spectroscopy [18,26] have been used. In several studies, XPS has been employed to study the dispersion and oxidation state of supported vanadia catalysts [27,28].…”

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“…It has been reported that the dispersed vanadia on the titania support enhanced the crystallization of TiO 2 . 10,11 A phase transformation of anatase to rutile is normally expected at 1073 K for TiO 2 with trace of V 2 O 5 . 10 In the present study, the calcination temperature was 723 K, with no indication of the rutile phase (JCPDS PDF No 76-1941).…”