Structure and reactivity of titania-supported oxides. Part 2: characterisation of various vanadium oxide on titania catalysts by x-ray photoelectron spectroscopy

Bond, Geoffrey C.; Zurita, Josefina Perez; Flamerz, S.

doi:10.1016/s0166-9834(00)82930-9

Cited by 109 publications

(33 citation statements)

References 8 publications

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“…This indirect method allows for evaluation of the fraction of accessible active phase atoms, but results may be complicated by the uncertainty of the extent of reduction of the active phase. In contrast, XPS can provide direct information on the dispersion of supported metal oxide catalysts [10] such as vanadia supported on SiO 2 , Al 2 O 3 [11] and TiO 2 [12]. Interestingly, in previous XPS studies on silica supported vanadia catalysts and vanadia-silica mixed oxide systems V species with V 2p 3/2 binding energies of up to 2 eV higher compared to those of reference compounds such as V 2 O 5 were found, which were attributed to vanadium species strongly interacting with silica [13][14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

The influence of water on the dispersion of vanadia supported on silica SBA-15

Heß

Schlögl

2006

Chemical Physics Letters

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The influence of water on the dispersion of silica SBA-15 supported vanadia model catalysts has been studied using X-ray photoelectron spectroscopy (XPS) as well as UV-VIS and Raman spectroscopy. XPS characterization of the V2p 3/2 state reveals the presence of two V 5+ states, which are assigned to vanadia with distinctly different cluster size. Upon dehydration a dramatic change in their intensity ratio is observed as a result of a substantial increase in the vanadia dispersion. It is shown that the observed changes in vanadia dispersion are directly associated with the changes in the molecular structure of the surface vanadia species.

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Section: Introductionmentioning

confidence: 99%

The influence of water on the dispersion of vanadia supported on silica SBA-15

Heß

Schlögl

2006

Chemical Physics Letters

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“…X-ray photoelectron spectroscopy (XPS) provides information about the oxidation state and the chemical environment of a given atom due to shifts in the binding energies [97][98][99][100][101][102][103][104][105]. The structural information is, however, limited since XPS cannot discriminate between different VO x structures possessing the same oxidation state, i.e.…”

Section: Bm Weckhuysen De Keller / Catalysis Today 78 (2003) 25-46mentioning

confidence: 99%

Chemistry, Spectroscopy and the Role of Supported Vanadium Oxides in Heterogeneous Catalysis

Weckhuysen

Keller

2003

ChemInform

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Supported vanadium oxide catalysts are active in a wide range of applications. In this review, an overview is given of the current knowledge available about vanadium oxide-based catalysts. The review starts with the importance of vanadium in heterogeneous catalysis, a discussion of the molecular structure of vanadium in water and in the solid state and an overview of the spectroscopic techniques enabling to study the chemistry of supported vanadium oxides. In the second part, it will be shown that advanced spectroscopic tools can be used to obtain detailed information about the coordination environment and oxidation state of vanadium oxides during each stage of the life-span of a heterogeneous catalyst. Three topics will be discussed: (1) the molecular structure of supported vanadium oxide catalysts under hydrated, dehydrated and reduced conditions, including the parameters, which influence the molecular structures formed at the surface of the support oxide; (2) elucidation of the active surface vanadium oxide during the oxidation of methanol to formaldehyde, the reaction mechanism and the vanadium oxide-support effect; and (3) deactivation of fluid catalytic cracking (FCC) catalysts by migration of vanadium oxides and the development of a method preventing the structural breakdown of zeolites by trapping the mobile vanadium oxides in an aluminum oxide coating.

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“…The nature of vanadium oxide species constituting the monolayer has been investigated by different techniques [4][5][6][7]. However thermal analysis was scarcely employed to characterize the V2Os/TiO2 systems [8,9].…”

mentioning

confidence: 99%

Thermal behaviour of high surface area V2O5/TiO2 catalysts

Turco

Bagnasco

Lisi

et al. 1992

Journal of Thermal Analysis

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Thermal analysis (TG and DTA) was employed for the characterization of V2Os/TiO2 catalysts supported on high surface urea TiO2. The results obtained are consistent with a uniform spreading of vanadium oxide on TiO2 surface for V205 content less than 15% by weight.The presence of V205 on the surface of TiO2 affects the anatase-rutile phase transition lowering the temperature at which it occurs.DTA measurements, performed on catalysts after many months from the preparation, show the appearance of an exothermic peak in the range 2g0~176This signal has been related to the oxidation of V(IV) to V(V) on the catalyst surface.Catalysts characterization, performed by chemical analysis and FT-IR spectroscopy, has confirmed this interpretation.It has been suggested that a slow modification of the catalyst occurs, leading to an increase of the V(IV) content during the time. The nature of vanadium oxide species constituting the monolayer has been investigated by different techniques [4][5][6][7]. However thermal analysis was scarcely employed to characterize the V2Os/TiO2 systems [8,9].In a recent work [10] we have studied chemical and physical properties of high surface area V2Os/TiO2 catalysts prepared by supporting V205 on laser synthesized ultrafine TiO2 powders. In this work we have employed the DTA and TG techniques in order to study the thermal stability of V2Os/TiO2 catalysts. Moreover, by such techniques, a further contribution to the characterization of vanadium oxide species formed on the catalyst surface has been achieved. ExperimentalThe V2Os/TiO2 catalysts were obtained by impregnation with NH4VO3 solution of high surface area (128 m2/g) TiO2 powder. The TiO2 support was synthesized by laser pyrolysis technique, as described in [11]. The catalysts were dried in oven at 120~ and then calcined at 400~ in air flow (99.95% purity) for 3 h. The catalysts contained V20~ nominal contents of 4, 8 and 15 wt%.The chemical analysis of V(IV) and V(V) was effected dissolving the catalysts in concentrated H2504 and titrating with KMnO4 to determine V(IV) content. The vanadium was reduced to +4 oxidation state with Fe(NHa)2(SO4)2.6H20 and then titrated with KMnO4 again to determine the total vanadium content.Thermal analysis was effected by using a DuPont 9000 system constituted by TG and DTA independent units. Both TG and DTA measurements were effected with heating rate of 20 deg/min. The reference for DTA measurements was TiO2 calcined at 1000~ which did not show any thermal effect in the whole range of temperature investigated.IR measurements were effected on a IFS 66 Bruker FT-IR apparatus using the KBr pellets technique. Results and discussionThe results were obtained on samples as synthesized and after different times from the synthesis.The results of chemical analysis of catalysts are reported in Table 1 as total vanadium and V(IV) content.The TG curves for pure TiO2 and for the catalysts after 1.5 years from the synthesis are shown in Fig. 1. It can be observed a large weight loss for all samples that starts at room te...

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Structure and reactivity of titania-supported oxides. Part 2: characterisation of various vanadium oxide on titania catalysts by x-ray photoelectron spectroscopy

Cited by 109 publications

References 8 publications

The influence of water on the dispersion of vanadia supported on silica SBA-15

The influence of water on the dispersion of vanadia supported on silica SBA-15

Chemistry, Spectroscopy and the Role of Supported Vanadium Oxides in Heterogeneous Catalysis

Thermal behaviour of high surface area V2O5/TiO2 catalysts

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