Solid-state NMR studies of silanol groups in mildly and highly dealuminated faujasites

E. F. Rakiewicz, Karl Todd Mueller, T. P. Jarvie, K. J. Sutovich, T. G. Roberie, A. W. Peters

Research output: Contribution to journalArticle

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Abstract

Experimental evidence for two different aluminum-bonded silanol species, Si(OSi)(OAl)2OH and Si(OSi)2(OAl)OH, in a mildly dealuminated faujasite is presented. A sample of a low unit cell size (Si/Al = 4.1) templated Y zeolite was prepared for this study to minimize interferences from framework structures highly-coordinated to aluminum, such as Si(OSi)(OAl)3 and Si(OAl)4. Bonding of the silicon to OH groups was observed by 1H/29Si cross-polarization/magic-angle-spinning NMR experiments, while bonding of silicon to aluminum was observed by 29Si/27Al dipolar-dephasing-difference NMR experiments. The newly identified sites are of interest because these aluminum-bonded silanol sites may dehydrate to form strong Brønsted or Lewis acid sites and thus change the activity of the zeolite in FCC catalysts. Strong Lewis acid sites have been implicated as a source of enhanced cracking activity for mildly dealuminated samples of both ZSM-5 and faujasite in previous studies. As an extension of these studies, the structure of a highly dealuminated faujasite by solid-state 29Si NMR methods was also examined. Our purpose is to resolve conflicting chemical shift assignments in the literature. Based on the results of a variable-contact-time 1H/29Si cross-polarization experiment, new signals with chemical shifts of -102 and -104 ppm are assigned to silicon atoms that are directly connected through bridging oxygen atoms to silicon atoms in silanol groups.

Original languageEnglish (US)
Pages (from-to)81-88
Number of pages8
JournalMicroporous Materials
Volume7
Issue number2-3
DOIs
StatePublished - Jan 1 1996

Fingerprint

Silicon
Aluminum
Nuclear magnetic resonance
solid state
aluminum
Zeolites
Lewis Acids
nuclear magnetic resonance
cross polarization
Chemical shift
silicon
Atoms
chemical equilibrium
Polarization
acids
Magic angle spinning
Acids
Experiments
metal spinning
atoms

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Materials Science(all)
  • Engineering(all)

Cite this

Rakiewicz, E. F., Mueller, K. T., Jarvie, T. P., Sutovich, K. J., Roberie, T. G., & Peters, A. W. (1996). Solid-state NMR studies of silanol groups in mildly and highly dealuminated faujasites. Microporous Materials, 7(2-3), 81-88. https://doi.org/10.1016/0927-6513(96)00031-4
Rakiewicz, E. F. ; Mueller, Karl Todd ; Jarvie, T. P. ; Sutovich, K. J. ; Roberie, T. G. ; Peters, A. W. / Solid-state NMR studies of silanol groups in mildly and highly dealuminated faujasites. In: Microporous Materials. 1996 ; Vol. 7, No. 2-3. pp. 81-88.
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Rakiewicz, EF, Mueller, KT, Jarvie, TP, Sutovich, KJ, Roberie, TG & Peters, AW 1996, 'Solid-state NMR studies of silanol groups in mildly and highly dealuminated faujasites', Microporous Materials, vol. 7, no. 2-3, pp. 81-88. https://doi.org/10.1016/0927-6513(96)00031-4

Solid-state NMR studies of silanol groups in mildly and highly dealuminated faujasites. / Rakiewicz, E. F.; Mueller, Karl Todd; Jarvie, T. P.; Sutovich, K. J.; Roberie, T. G.; Peters, A. W.

In: Microporous Materials, Vol. 7, No. 2-3, 01.01.1996, p. 81-88.

Research output: Contribution to journalArticle

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T1 - Solid-state NMR studies of silanol groups in mildly and highly dealuminated faujasites

AU - Rakiewicz, E. F.

AU - Mueller, Karl Todd

AU - Jarvie, T. P.

AU - Sutovich, K. J.

AU - Roberie, T. G.

AU - Peters, A. W.

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Y1 - 1996/1/1

N2 - Experimental evidence for two different aluminum-bonded silanol species, Si(OSi)(OAl)2OH and Si(OSi)2(OAl)OH, in a mildly dealuminated faujasite is presented. A sample of a low unit cell size (Si/Al = 4.1) templated Y zeolite was prepared for this study to minimize interferences from framework structures highly-coordinated to aluminum, such as Si(OSi)(OAl)3 and Si(OAl)4. Bonding of the silicon to OH groups was observed by 1H/29Si cross-polarization/magic-angle-spinning NMR experiments, while bonding of silicon to aluminum was observed by 29Si/27Al dipolar-dephasing-difference NMR experiments. The newly identified sites are of interest because these aluminum-bonded silanol sites may dehydrate to form strong Brønsted or Lewis acid sites and thus change the activity of the zeolite in FCC catalysts. Strong Lewis acid sites have been implicated as a source of enhanced cracking activity for mildly dealuminated samples of both ZSM-5 and faujasite in previous studies. As an extension of these studies, the structure of a highly dealuminated faujasite by solid-state 29Si NMR methods was also examined. Our purpose is to resolve conflicting chemical shift assignments in the literature. Based on the results of a variable-contact-time 1H/29Si cross-polarization experiment, new signals with chemical shifts of -102 and -104 ppm are assigned to silicon atoms that are directly connected through bridging oxygen atoms to silicon atoms in silanol groups.

AB - Experimental evidence for two different aluminum-bonded silanol species, Si(OSi)(OAl)2OH and Si(OSi)2(OAl)OH, in a mildly dealuminated faujasite is presented. A sample of a low unit cell size (Si/Al = 4.1) templated Y zeolite was prepared for this study to minimize interferences from framework structures highly-coordinated to aluminum, such as Si(OSi)(OAl)3 and Si(OAl)4. Bonding of the silicon to OH groups was observed by 1H/29Si cross-polarization/magic-angle-spinning NMR experiments, while bonding of silicon to aluminum was observed by 29Si/27Al dipolar-dephasing-difference NMR experiments. The newly identified sites are of interest because these aluminum-bonded silanol sites may dehydrate to form strong Brønsted or Lewis acid sites and thus change the activity of the zeolite in FCC catalysts. Strong Lewis acid sites have been implicated as a source of enhanced cracking activity for mildly dealuminated samples of both ZSM-5 and faujasite in previous studies. As an extension of these studies, the structure of a highly dealuminated faujasite by solid-state 29Si NMR methods was also examined. Our purpose is to resolve conflicting chemical shift assignments in the literature. Based on the results of a variable-contact-time 1H/29Si cross-polarization experiment, new signals with chemical shifts of -102 and -104 ppm are assigned to silicon atoms that are directly connected through bridging oxygen atoms to silicon atoms in silanol groups.

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Rakiewicz EF, Mueller KT, Jarvie TP, Sutovich KJ, Roberie TG, Peters AW. Solid-state NMR studies of silanol groups in mildly and highly dealuminated faujasites. Microporous Materials. 1996 Jan 1;7(2-3):81-88. https://doi.org/10.1016/0927-6513(96)00031-4