Structure of molybdenum oxide supported on silica SBA-15 studied by Raman, UV–Vis and X-ray absorption spectroscopy

Thielemann, Jörg P.; Ressler, Thorsten; Walter, Anke; Tzolova-Müller, Genka; Heß, Christian

doi:10.1016/j.apcata.2011.03.032

Cited by 100 publications

(80 citation statements)

References 66 publications

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“…250 and 360 nm. attributed to octahedral (O h ) tungsten species in accord with literature data [33,34]. Both encapsulated and impregnated catalysts displayed quite the same patterns with two bands at ca.…”

Section: Structural State Of the Hpa In The Catalystssupporting

confidence: 74%

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Comparison of the Acidity of Heteropolyacids Encapsulated in or Impregnated on SBA-15

Pinto

Szeto

Oueslati

et al. 2016

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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-Heteropolyacids (HPA) immobilized onto SBA-15 silica were prepared by two different ways using either impregnation or encapsulation methodologies. Two Keggin-type HPA, H 3 PW 12 O 40 and H 4 SiW 12 O 40 were considered in this study. The resulting hybrid materials were fully characterized by N 2 adsorption-desorption isotherms, XRD, FT-IR, Raman, diffuse reflectance UV-Vis spectroscopies and 31 P MAS NMR. All characterization methods showed that at room temperature the catalysts contained well-dispersed and intact Keggin units throughout the solid. The catalytic activity of these solids was investigated in the isomerization of n-hexane. The impregnated and encapsulated phosphotungstic catalysts performed similarly in catalysis showing that the amount of active sites was nearly the same in both catalysts. On the contrary, the tungstosilicic encapsulated material was completely inactive while its impregnated counterpart was even more active than the phosphotungstic derived catalysts. The acidity of the solids was measured by various methods: microcalorimetry of ammonia adsorption, ammonia desorption followed by Temperature Programmed Desorption (TPD) and DRIFT/GC-MS and pyridine adsorption followed by infrared spectroscopy. Only pyridine adsorption and ammonia desorption followed by DRIFT/GC-MS agreed with the catalytic data. Ammonia adsorption followed by microcalorimetry was not able to differentiate between the four catalysts while the TPD experiments led to unreliable results, as not only the evolved ammonia but also other molecules such as water were taken into account in the measurements. The behavior difference between the encapsulated silico-and phosphotungstic acids was explained by a more pronounced encapsulation in the case of silicon. de préparation. L'activité catalytique de ces matériaux a ensuite été étudiée dans l'isomérisation du n-hexane.

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Section: Structural State Of the Hpa In The Catalystssupporting

confidence: 74%

“…W 6+ intraframework (W 12 O 36 ) charge transfer in the highly dispersed Keggin units. All HPA supported catalysts showed shifted signals with regards to pure HPA indicating a change in the symmetry, the interactions with the support decreasing the tetrahedral symmetry of the Keggin units [33,34].…”

Section: Structural State Of the Hpa In The Catalystsmentioning

confidence: 99%

Comparison of the Acidity of Heteropolyacids Encapsulated in or Impregnated on SBA-15

Pinto

Szeto

Oueslati

et al. 2016

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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“…This indicated structural changes from octahedral to tetrahedral [MO x ]( M = V, Mo) units during thermal treatment under catalytic conditions. [22,23] The evolution of the normalized pre-edge peak height together with the ion currents of H 2 O, CO, CO 2 ,a crolein, and acetone during the oxidation of propene is shown in Figure 5b )o factivated PV 2 Mo 10 -SBA-15 exhibited features similart ot hat of previously reported dehydrated molybdenum oxidesa nd HPOMs supported on SBA-15. [18,23] For am ore detailed analysis, hexagonal MoO 3 was used as astructuralmodel.Theoretical X-ray absorption fine structure (XAFS) phases and amplitudes were calculated for MoÀOa nd MoÀMo distances and used fore xtended X- Hence, isolated tetrahedral [MoO 4 ]u nits can be excluded as major molybdenum oxide species.…”

supporting

confidence: 57%

“…[22,23] The evolution of the normalized pre-edge peak height together with the ion currents of H 2 O, CO, CO 2 ,a crolein, and acetone during the oxidation of propene is shown in Figure 5b )o factivated PV 2 Mo 10 -SBA-15 exhibited features similart ot hat of previously reported dehydrated molybdenum oxidesa nd HPOMs supported on SBA-15. [18,23] For am ore detailed analysis, hexagonal MoO 3 was used as astructuralmodel.Theoretical X-ray absorption fine structure (XAFS) phases and amplitudes were calculated for MoÀOa nd MoÀMo distances and used fore xtended X- Hence, isolated tetrahedral [MoO 4 ]u nits can be excluded as major molybdenum oxide species. [24] Linear combinations of the XANES spectra of Na 2 The evolution of the average local structure aroundVc enters in the supported catalysts and reference materials differed from that aroundM oc enters.…”

supporting

confidence: 57%

Role of Vanadium and Phosphorus in Substituted Keggin‐Type Heteropolyoxo Molybdates Supported on Silica SBA‐15 in Selective Propene Oxidation

2015

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Vanadium‐containing Keggin‐type heteropolyoxo molybdate ([PV2Mo10O40]5−) was supported on silica SBA‐15 (denoted as PV2Mo10‐SBA‐15). The structural evolution and catalytic activity of PV2Mo10‐SBA‐15 and a suitable reference V2Mo10Ox‐SBA‐15 were investigated under selective propene oxidation conditions by using in situ X‐ray absorption spectroscopy. 31P MAS NMR measurements of supported PV2Mo10‐SBA‐15 and reference H3PO4‐SBA‐15 were performed after the catalytic reaction. PV2Mo10‐SBA‐15 formed a mixture of mainly tetrahedral [MoOx] and [VOx] units during thermal treatment under propene oxidation conditions. Changes in the average local structure around V centers coincided with the changes in the average local structure around Mo centers and the onset of catalytic activity. In addition, mainly tetrahedral [MoOx] and [VOx] units seemed to be in close proximity and interacted under catalytic conditions. Conversely, in the reference material V2Mo10Ox‐SBA‐15 synthesized with individual V and Mo source precursors, Mo and V centers appeared to be more separated from each other. The structural environment of P in PV2Mo10‐SBA‐15 under catalytic conditions corresponded to a mixture of various species. P was connected to both the support material SBA‐15 via POSi bonds and [MoOx] or [VOx] units. Apparently, the proximity of V and Mo in Keggin precursors was a prerequisite for obtaining (Mo,V) oxide species on the support material.

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“…Typically three kinds of Cr species, i.e., isolated monochromate, polychromate, and crystalline Cr 2 O 3 are seen in supported chromia catalysts. The Raman spectrum of SBA-15 shows three bands at 497, 607 and 977 cm -1 assigned to cyclic tetrasiloxane rings, cyclic trisiloxane rings and the Si-OH stretching mode, respectively [34]. It can be seen that the spectra of chromium-incorporated samples exhibit a band at 987 cm -1 assigned to the t s (O=Cr=O) stretching, the other at 394 cm -1 due to d(O=Cr=O) bending, and finally, the band at 1014 cm -1 referred to t(O=Cr=O) stretching, as reported by Dines Fig.…”

Section: Laser-raman Resultsmentioning

confidence: 99%

Oxidative dehydrogenation of ethane with carbon dioxide over Cr2O3/SBA-15 catalysts: the influence of sulfate modification of the support

et al. 2017

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Unmodified and sulfate-modified SBA-15-supported Cr 2 O 3 catalysts were prepared by impregnation method. The physico-chemical properties of the supports and catalysts were determined by nitrogen adsorption/ desorption, powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), laser-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (UV-DRS), inductively coupled plasma optical emission spectroscopy (ICP-OES), transmission electron microscopy (TEM) and temperature-programmed reduction (TPR) techniques. Oxidative dehydrogenation of ethane to ethylene (ODE) with CO 2 as oxidant was carried out on these catalysts in a fixed-bed reactor at temperatures in the range of 600-700°C and at atmospheric pressure. The changes in structural and textural properties because of sulfate modification were identified. Sulfate modification affected the nature of interaction of CrO x species with the SBA-15 support. During the evaluation, it was observed that sulfate modification enhances ethane conversion and ethylene selectivity of the catalyst. Better dispersion of CrO x and the increase in Cr 6? /Cr 3? ratio seem to be the reasons for the higher performance of the sulfate-modified catalysts compared to that of the unmodified catalyst.

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Structure of molybdenum oxide supported on silica SBA-15 studied by Raman, UV–Vis and X-ray absorption spectroscopy

Cited by 100 publications

References 66 publications

Comparison of the Acidity of Heteropolyacids Encapsulated in or Impregnated on SBA-15

Comparison of the Acidity of Heteropolyacids Encapsulated in or Impregnated on SBA-15

Role of Vanadium and Phosphorus in Substituted Keggin‐Type Heteropolyoxo Molybdates Supported on Silica SBA‐15 in Selective Propene Oxidation

Oxidative dehydrogenation of ethane with carbon dioxide over Cr2O3/SBA-15 catalysts: the influence of sulfate modification of the support

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