Catalytically Active Sites: Generation and Characterization

Hunger, Michael

doi:10.1002/9783527630295.ch17

Cited by 29 publications

(41 citation statements)

References 291 publications

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“…partially dislodged TFAl species, which also cannot be leached out using HNO 3 42,58. Al K-edge XANES confirm the removal of {Al} EF species as the peak at 1568 eV disappears.Furthermore, there is an increase in the ratio between the 3603 cm -1 and 3660 cm -1 band in the FT-IR spectra, which is in accordance with the removal of {Al} EF species 57. One could deduce from the FT-IR spectra that sample [MOR] 400-L contains more bridging hydroxyl groups.However, pyridine chemisorption experiments did not show an appreciable difference in the Brønsted acid site number as shown inFigure S8.…”

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confidence: 50%

“…55,56 Furthermore, {Al} EF species can be observed as the peak at 1568.6 eV (+3.6 eV) in the Al K-edge XANES in Figure 5 b 25,33 FT-IR spectroscopy shows that dealumination leads to a reduction in Brønsted acid sites as the band 3603 cm -1 that corresponds to bridging hydroxyl groups decreases in intensity (Figure 5 c). 57 The band at 3660 cm -1 corresponds to Al-OH groups 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 20 in {Al} EF . 57 N 2 -physisorption data presented in Figure S5 and Table S1 indicates a decreased pore volume, no indication of the formation of mesopores and XRD data shows that the crystalline structure of the MOR framework remains intact.…”

Section: Reaction Between Extra-framework Aluminum Oxide Hydroxide Anmentioning

confidence: 97%

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Aluminum-Phosphate Binder Formation in Zeolites as Probed with X-ray Absorption Microscopy

et al. 2014

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In this work, three industrially relevant zeolites with framework topologies of MOR, FAU and FER have been explored on their ability to form an AlPO4 phase by reaction of a phosphate precursor with expelled framework aluminum. A detailed study was performed on zeolite H-mordenite, using in situ STXM and soft X-ray absorption tomography, complemented with (27)Al and (31)P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, XRD, FT-IR spectroscopy, and N2 physisorption. Extraframework aluminum was extracted from steam-dealuminated H-mordenite and shown to dominantly consist of amorphous AlO(OH). It was found that phosphoric acid readily reacts with the AlO(OH) phase in dealuminated H-mordenite and forms an extraframework amorphous AlPO4 phase. It was found that while AlPO4 crystallizes outside of the zeolitic channel system forming AlPO4 islands, AlPO4 that remains inside tends to stay more amorphous. In the case of ultrastable zeolite Y the FAU framework collapsed during phosphatation, due to extraction of framework aluminum from the lattice. However, using milder phosphatation conditions an extraframework AlPO4 α-cristobalite/tridymite phase could also be produced within the FAU framework. Finally, in steamed zeolite ferrierite with FER topology the extraframework aluminum species were trapped and therefore not accessible for phosphoric acid; hence, no AlPO4 phase could be formed within the structure. Therefore, the parameters to be taken into account in AlPO4 synthesis are the framework Si/Al ratio, stability of framework aluminum, pore dimensionality and accessibility of extraframework aluminum species.

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confidence: 50%

Section: Reaction Between Extra-framework Aluminum Oxide Hydroxide Anmentioning

confidence: 97%

Aluminum-Phosphate Binder Formation in Zeolites as Probed with X-ray Absorption Microscopy

et al. 2014

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“…These bands correspond to internal silanol groups, external silanol groups and external Al-OH groups, respectively. 34 The FT-IR spectrum of adsorbed pyridine, presented in Fig. S1 (ESI †), indicates that the sample contains both Brønsted acid sites and Lewis acid sites.…”

Section: Effect Of Thermal and Acid Treatmentmentioning

confidence: 99%

Local silico-aluminophosphate interfaces within phosphated H-ZSM-5 zeolites

Bij

Weckhuysen

2014

Phys. Chem. Chem. Phys.

127

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In order to elucidate phosphorus-zeolite H-ZSM-5 interactions, a variety of phosphorus-modified zeolite H-ZSM-5 materials were studied in a multi-spectroscopic manner. By deploying single pulse 27 Al, 31 P MAS NMR, 2D heteronuclear 27 Al-31 P correlation (HETCOR), 27 Al MQ MAS NMR spectroscopy, TPD of pyridine monitored by FT-IR spectroscopy, and Scanning Transmission X-ray Microscopy (STXM) the interplay and influence of acidity, thermal treatment and phosphorus on the structure and acidity of H-ZSM-5 were established. It was found that while acid treatment did not affect the zeolite structure, thermal treatment leads to the breaking of Si-OH-Al bonds, a decrease in the strong acid site number and the formation of terminal Al-OH groups. No extra-framework aluminium species was observed. Phosphorus precursors interact with the zeolitic framework through hydrogen bonds and physical coordination, as phosphorus species can be simply washed out with hot water. After phosphatation and thermal treatment two effects occur simultaneously, namely (i) phosphorus species transform into water insoluble condensed poly-phosphoric acid and (ii) phosphoric acid binds irreversibly to the terminal Al-OH groups of partially dislodged four-coordinated framework aluminium, forming local silico-aluminophosphate interfaces.These interfaces are potentially the promoters of hydrothermal stability in phosphated zeolite H-ZSM-5.

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“…Sample [Z] exhibits a very strong band at 3604 cm −1 and a smaller peak at 3736 cm −1 . These bands are attributed to bridging hydroxyl groups (SiOHAl) and external silanol groups, respectively 58. Two less distinct bands are observed at 3620 cm −1 , stemming from internal silanol groups, and at 3780 cm −1 , corresponding to external AlOH groups 58.…”

Section: Resultsmentioning

confidence: 99%

“…These bands are attributed to bridging hydroxyl groups (SiOHAl) and external silanol groups, respectively 58. Two less distinct bands are observed at 3620 cm −1 , stemming from internal silanol groups, and at 3780 cm −1 , corresponding to external AlOH groups 58. After phosphatation ( P[Z] ) there is a sharp decrease in the amount of bridging hydroxyl groups.…”

Section: Resultsmentioning

confidence: 99%

Vorschau auf Heft 5/2015

2015

Chemie in nserer Zeit

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Catalytically Active Sites: Generation and Characterization

Cited by 29 publications

References 291 publications

Aluminum-Phosphate Binder Formation in Zeolites as Probed with X-ray Absorption Microscopy

Aluminum-Phosphate Binder Formation in Zeolites as Probed with X-ray Absorption Microscopy

Local silico-aluminophosphate interfaces within phosphated H-ZSM-5 zeolites

Vorschau auf Heft 5/2015

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