Physical and chemical characterization of surface vanadium oxide supported on titania: influence of the titania phase (anatase, rutile, brookite and B)

Deo, Goutam; Turek, Andrzej M.; Wachs, Israel E.; Machej, T.; Haber, J.; Das, Nandini; Eckert, Hellmut; Hirt, Andrew M.

doi:10.1016/0926-860x(92)85176-c

Cited by 133 publications

(84 citation statements)

References 34 publications

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“…This band is attributed to VdO symmetric stretching vibrations (1) in isolated VO 4 units on anatase. 6,18 Also shown in Figure 1 is the infrared spectrum of V/TiO 2 taken after dehydration. The peak at 2051 cm -1 , which is not observed for TiO 2 , is assigned to the overtone of the symmetric stretch of VdO in isolated VO 4 units of the support.…”

Section: Resultsmentioning

confidence: 99%

“…[1][2][3] Characterization of the vanadate centers by multiple techniques has demonstrated that at low vanadium coverages the supported VO 4 species have a distorted tetrahedral geometry containing a single VdO bond and three V-O-M bonds (M ) support metal), irrespective of support composition. [4][5][6][7] The composition of the support, however, has a large effect on catalyst activity. For example, it has been reported that the activity of VO x /TiO 2 is 3 orders of magnitude higher than that of VO x /SiO 2 under comparable reaction conditions.…”

Section: Introductionmentioning

confidence: 99%

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Mechanistic Studies of Methanol Oxidation to Formaldehyde on Isolated Vanadate Sites Supported on High Surface Area Anatase

2007

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The mechanism for methanol oxidation on both TiO 2 and V/TiO 2 was investigated using temperatureprogrammed experiments with in-situ infrared spectroscopy. Infrared and Raman spectroscopy, along with XANES, show that the V/TiO 2 sample consists predominantly of isolated VO 4 units after calcination. Methanol was found to adsorb on the catalyst in three ways at 323 K: (1) molecularly, (2) across Ti-O-Ti bonds to form Ti-OCH 3 /Ti-OH pairs, and (3) across V-O-Ti bonds to form V-OCH 3 /Ti-OH pairs. Upon heating, two desorption peaks for CH 3 OH and H 2 O were observed on all samples below 500 K. Although TiO 2 produced small amounts of CH 2 O, the addition of vanadium greatly enhanced the rate of formaldehyde formation. Also, on the V/TiO 2 samples, it was noticed that the Ti-OCH 3 groups disappear much more rapidly than on TiO 2 alone. This is likely due to the reverse spillover of methoxide species from Ti to V, with the reaction occurring at lower temperatures at the vanadium center. Formate species were also detected during the experiments, and they are assumed to be intermediates in the decomposition of formaldehyde to CO, CO 2 , and H 2 O. The apparent activation energy of V/TiO 2 for the formation of CH 2 O is 16 kcal/mol.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mechanistic Studies of Methanol Oxidation to Formaldehyde on Isolated Vanadate Sites Supported on High Surface Area Anatase

2007

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“…The molecular structure of these supported vanadium oxide species has been studied by a wide variety of spectroscopic techniques, including Raman, 51 V NMR, UV-vis-near-infrared, extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge spectroscopy, electron spin resonance, and X-ray photoelectron spectroscopy. [5][6][7][8][9][10][11][12][13][14][15][16][17][18] Several review papers, which describe the current understanding of these catalytic systems, [18][19][20][21] can be found in the literature.…”

Section: Introductionmentioning

confidence: 99%

Determining the Structure of Silica-Supported Monomeric Vanadium Oxide Catalysts Based on Synthesis Method and Spectral Data from Theoretical Calculations

et al. 2007

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Infrared and Raman spectra have been calculated for several molecular cluster models for the silica-supported monomeric vanadium oxide catalysts that are proposed in the literature: the pyramid model, the umbrella model, and a model containing two bonds to the support, a VdO group and an OH group. A related model with one bond to the support, a VdO and two OH groups, will also be discussed. From the comparison with literature, it is concluded that two models, the umbrella model and the model with two bonds to the support, are realistic descriptions of actual systems. The presence of a particular compound depends on the method of preparation. The internal V-O distances by themselves are not enough to distinguish between the presented models.

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“…For high temperature applications of titania as catalysts, membranes, and sensors, a stable anatase phase is necessary. 8 Therefore, one of the problems in both catalytic and sensor applications of anatase-based material is its transformation to rutile, a process that depends on both temperature and time. [9][10][11] The presence of a suitable doping agent strongly affects the kinetics of this process.…”

Section: Introductionmentioning

confidence: 99%

Effects of Nb doping on the TiO2 anatase-to-rutile phase transition

Arbiol

Cerdá

Dezanneau

et al. 2002

Journal of Applied Physics

306

184

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We study the influence of Nb doping on the TiO 2 anatase-to-rutile phase transition, using combined transmission electron microscopy, Raman spectroscopy, x-ray diffraction and selected area electron diffraction analysis. This approach enabled anatase-to-rutile phase transition hindering to be clearly observed for low Nb-doped TiO 2 samples. Moreover, there was clear grain growth inhibition in the samples containing Nb. The use of high resolution transmission electron microscopy with our samples provides an innovative perspective compared with previous research on this issue. Our analysis shows that niobium is segregated from the anatase structure before and during the phase transformation, leading to the formation of NbO nanoclusters on the surface of the TiO 2 rutile nanoparticles.

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Physical and chemical characterization of surface vanadium oxide supported on titania: influence of the titania phase (anatase, rutile, brookite and B)

Cited by 133 publications

References 34 publications

Mechanistic Studies of Methanol Oxidation to Formaldehyde on Isolated Vanadate Sites Supported on High Surface Area Anatase

Mechanistic Studies of Methanol Oxidation to Formaldehyde on Isolated Vanadate Sites Supported on High Surface Area Anatase

Determining the Structure of Silica-Supported Monomeric Vanadium Oxide Catalysts Based on Synthesis Method and Spectral Data from Theoretical Calculations

Effects of Nb doping on the TiO2 anatase-to-rutile phase transition

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