1H and 31P MAS NMR studies of solid heteropolyacids and H3PW12O40 supported on SiO2

Мастихин, В. М.; Куликов, С. М.; Носов, А. В.; Kozhevnikov, I. V.; Mudrakovsky, I. L.; Timofeeva, Maria N.

doi:10.1016/0304-5102(90)85068-s

Cited by 152 publications

(50 citation statements)

References 4 publications

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“…Indeed the ratio of bulk : perturbed W atoms of $3:1 is consistent with an adsorption geometry in which each Keggin unit binds to the silica through 3 terminal W@O bonds. Whilst interactions of this type have been speculated [8,11] this represents the first spectroscopic evidence in support of such a bonding mode.…”

Section: Evolution Of Surface Speciesmentioning

confidence: 83%

“…It has been hypothesised that in the initial stages of impregnation, the HPA material reacts with a hydroxylated silica surface to form an ion pair with one or more silanol via simple proton transfer, possibly involving dehydration: ðBSiOH 2 Þ þ ðH 2 PW 12 O 40 Þ À [8][9][10] or ðBSiÞ þ m ðH 3Àm PW 12 O 40 Þ mÀ þ mH 2 O [8,11] However attempts to discern these surface HPA species using 31 P-MAS NMR (a non-surface sensitive technique) have proven inconclusive [1,3,9,11].…”

Section: Introductionmentioning

confidence: 99%

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On the active site in H3PW12O40/SiO2 catalysts for fine chemical synthesis

et al. 2005

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The surface environment and structural evolution of silica supported phosphotungstic acid (H 3 PW 12 O 40 ) catalysts have been investigated as a function of acid loading. H 3 PW 12 O 40 clusters are deposited intact upon the silica surface, adopting a StranksiKrastanov growth mode forming a two-dimensional adlayer which saturates at 45wt% acid. Intimate contact with the silica support perturbs the local chemical environment of three tungstate centres, which become inequivalent with those in the remaining cluster, suggesting an adsorption mode involving three terminal W@O groups. Above the monolayer, H 3 PW 12 O 40 clusters form threedimensional crystallites with physico-chemical properties indistinguishable from those in the bulk heteropoly acid. These H 3 PW 12 O 40 /SiO 2 materials are efficient for the solventless isomerisation of a-pinene under mild reaction conditions. Activity scales directly with the number of accessible perturbed tungstate sites at the silica interface; these are the active species.

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Section: Evolution Of Surface Speciesmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 99%

On the active site in H3PW12O40/SiO2 catalysts for fine chemical synthesis

et al. 2005

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“…The interaction of Keggin ions with hydroxyls is known to lead to the formation of distorted grafted HPA compounds even with weak bases such as SiO 2 or MCM-41 [13,16,17]. The grafted (MOH 2 + )(H 2 PW 12 O 40 − ) species were found to be the main states of HPW supported in low concentration on the oxide surface among of bulk crystalline form.…”

Section: Introductionmentioning

confidence: 97%

Isomerization of n-hexane on the Pt-promoted Keggin and Dawson tungstophosphoric heteropoly acids supported on zirconia

Иванов

Vasina

Ниссенбаум

et al. 2004

Applied Catalysis A: General

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“…Based on microcalorimetry measurements of the heat of adsorption of NH 3 , Kozhevnikov and coworkers [23] reported that the acid strength of TPA decreased significantly when supported on SiO 2 . Other reports [24,25] indicate that protons of TPA react with OH groups on SiO 2 to form -OH 2? (H 2 PW 12 O 40 -).…”

Section: Characterization Of the Samplesmentioning

confidence: 98%

The Support Effect over Pt–H3PW12O40 Based Metal-Acid Bifunctional Catalysts on the Catalytic Performance in n-Pentane Isomerization

Zhang

et al. 2008

Catal Lett

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The effects of the support materials (c-Al 2 O 3 , SiO 2 , ZrO 2 ) on the catalytic performance in n-pentane isomerization have been investigated for Pt-H 3 PW 12 O 40 (Pt-TPA) metal-acid bifunctional catalysts. Significant impact of supports on the catalyst activity has been found and the activity sequence corresponding to different supports was ZrO 2 [ [SiO 2 [ [c-Al 2 O 3 . Several characterization methods of XRD, FT-IR, NH 3 -TPD, TPR and BET were used to explore the nature of the supported catalysts. Simultaneously, the influence of a series of pretreatment conditions of pH, calcination temperature and calcination time for self-prepared ZrO 2 on the catalytic performance related to the supported Pt-TPA catalysts was studied.

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1H and 31P MAS NMR studies of solid heteropolyacids and H3PW12O40 supported on SiO2

Cited by 152 publications

References 4 publications

On the active site in H3PW12O40/SiO2 catalysts for fine chemical synthesis

On the active site in H3PW12O40/SiO2 catalysts for fine chemical synthesis

Isomerization of n-hexane on the Pt-promoted Keggin and Dawson tungstophosphoric heteropoly acids supported on zirconia

The Support Effect over Pt–H3PW12O40 Based Metal-Acid Bifunctional Catalysts on the Catalytic Performance in n-Pentane Isomerization

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