Stability of Ti in MFI and Beta structures: a comparative study

Carati, Angela; Flego, C.; Massara, Elisabetta Previde; Millini, Roberto; Carluccio, Luciano C.; Parker, Wallace O.; Bellussi, Giuseppe

doi:10.1016/s1387-1811(99)00018-9

Cited by 98 publications

(48 citation statements)

References 13 publications

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“…The band at 330 nm generally associated with TiO 2 clusters is not observed suggesting that the latter are not present, in line with earlier data on Ti BEA and TiMFI [26], TiMCM-41 [27] and TiSilicalite [28]. In the spectrum of Ti 5.8 SiBEA, an intense and asymmetric band at 230 nm appears which is assigned to the oxygen-tetrahedral Ti(IV) LMCT transition [11,[23][24][25][26][27][28] and confirms the incorporation of Ti atoms into the SiBEA framework. The shoulder at 265 nm could be attributed to octahedral Ti(IV) in framework and/or extraframework position similarly as the band at *290 nm observed for Ti 1.5 SiBEA and Ti 3.2 SiBEA.…”

Section: Diffuse Reflectance Uv-vis Spectroscopysupporting

confidence: 88%

Section: Diffuse Reflectance Uv-vis Spectroscopysupporting

confidence: 66%

“…4) exhibit two bands at about 220 and 290 nm assigned to oxygen-tetrahedral Ti(IV) and oxygen-octahedral Ti(IV) ligand to metal charge transfer (LMCT) transitions, respectively, as reported earlier for TiBEA and TiMCM-41 materials [11,[23][24][25][26][27]. The band at 330 nm generally associated with TiO 2 clusters is not observed suggesting that the latter are not present, in line with earlier data on Ti BEA and TiMFI [26], TiMCM-41 [27] and TiSilicalite [28]. In the spectrum of Ti 5.8 SiBEA, an intense and asymmetric band at 230 nm appears which is assigned to the oxygen-tetrahedral Ti(IV) LMCT transition [11,[23][24][25][26][27][28] and confirms the incorporation of Ti atoms into the SiBEA framework.…”

Section: Diffuse Reflectance Uv-vis Spectroscopysupporting

confidence: 66%

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Nature, Environment and Quantification of Titanium Species in TiSiBEA Zeolites Investigated by XRD, NMR, DR UV–Vis and XPS

et al. 2009

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Ti x SiBEA zeolites (x = 1.5, 3.2 and 5.8 Ti wt%) are prepared by a two-step postsynthesis method involving (1) dealumination of TEABEA zeolite by nitric acid leading to nests of SiO-H groups in vacant T-atom sites and (2) incorporation of Ti into SiBEA zeolite by reacting TiCl 4 vapor with those silanol groups. The incorporation of Ti into the SiBEA framework is evidenced by XRD, 29 Si MAS NMR, 1 H-29 Si CP MAS NMR and 1 H MAS NMR. DR UV-vis and XPS investigations show that, for low Ti content, mainly framework tetrahedral Ti(IV) ions are present in Ti x SiBEA zeolites. On the basis of XPS data, the quantification of framework tetrahedral Ti(IV) and framework and/ or extra-framework octahedral Ti(IV) ions is followed as a function of Ti content.

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Section: Diffuse Reflectance Uv-vis Spectroscopysupporting

confidence: 88%

Section: Diffuse Reflectance Uv-vis Spectroscopysupporting

confidence: 66%

Section: Diffuse Reflectance Uv-vis Spectroscopysupporting

confidence: 66%

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Nature, Environment and Quantification of Titanium Species in TiSiBEA Zeolites Investigated by XRD, NMR, DR UV–Vis and XPS

et al. 2009

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“…It is a matter of fact that titanium is tetrahedrally coordinated in well-manufactured Ti,Si-catalysts, while it certainly has an octahedral-like geometry in Ti-POMs. However, we have to emphasise that numerous DR-UV, XANES and EXAFS studies performed on titanium-silicates have revealed that in the presence of water, which always accompanies H 2 O 2 , tetrahedral titanium ions coordinate H 2 O and consequently are transformed into pentahedral and/or octahedral ones [80,87,[138][139][140].…”

Section: Comparison Of Catalytic Behaviour Of Ti-poms and Heterogeneomentioning

confidence: 99%

Titanium-monosubstituted polyoxometalates: relation between homogeneous and heterogeneous Ti-single-site-based catalysis

Kholdeeva

2006

Top Catal

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“…The difference of our experimental results from those of Haanepen and co-workers might be due to the different substrates. Cyclohexane is an apolar molecule, while both 3-phenyl-2-propen-1-ol and 3-octanol are large polar molecules, which could extract framework metal ions too [46,47]. Thus, more V 5+ ions would be leached in the reactant solution when oxidizing these bulky alcohols, resulting in a more apparent continuation of the reaction after the removal of the catalyst.…”

Section: Catalyst Testingmentioning

confidence: 99%

Synthesis, characterization and catalysis of (Co, V)-, (Co, Cr)- and (Cr, V)APO-5 molecular sieves

Fan

Song

et al. 2006

Microporous and Mesoporous Materials

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Synthesis, characterization and catalysis of (Co, V)-, (Co, Cr)-and (Cr, V)APO-5 molecular sieves ) molecular sieves have been hydrothermally synthesized and characterized. The as-synthesized and calcined samples were investigated with XRD, ICP, DRS UV-vis spectroscopy, ESR, 27 Al MAS NMR techniques to explore the valence, coordination and location of the incorporated transition metal ions. It was shown that isomorphous substitution of Co 2+ for Al 3+ convincingly occurred, and V 4+ also anchored to the sample by coordinating to two framework oxygen atoms and most probably occupying P 5+ sites, while no unambiguous spectroscopic evidence was provided for the incorporation of Cr 3+ in the lattice, although chemical analysis suggests this possibility in the case that Co 2+ or V 4+ are added to the synthesis gel. The preferential sequence for the incorporation of these transition metal ions in the AFI framework is: Co 2+ > V 4+ > Cr 3+ . After calcination, almost all V 4+ ions were oxidized to V 5+ , whereas Cr 3+ ions were oxidized to Cr 5+ and Cr 6+ . As catalysts, the (M, N)APO-5 molecular sieves are highly active for the selective oxidation of cyclohexane with a high cyclohexanone/cyclohexanol ratio in the presence of H 2 O 2 . The reaction temperature and solvent significantly influenced the catalytic behavior. Although some leaching of the transition metal ions was observed, the catalytic performance remained stable at least within five repeated runs.

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Stability of Ti in MFI and Beta structures: a comparative study

Cited by 98 publications

References 13 publications

Nature, Environment and Quantification of Titanium Species in TiSiBEA Zeolites Investigated by XRD, NMR, DR UV–Vis and XPS

Nature, Environment and Quantification of Titanium Species in TiSiBEA Zeolites Investigated by XRD, NMR, DR UV–Vis and XPS

Titanium-monosubstituted polyoxometalates: relation between homogeneous and heterogeneous Ti-single-site-based catalysis

Synthesis, characterization and catalysis of (Co, V)-, (Co, Cr)- and (Cr, V)APO-5 molecular sieves

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