Concentration and acid strength of hydroxyl groups in zeolites La,Na-X and La,Na-Y with different lanthanum exchange degrees studied by solid-state NMR spectroscopy

Jun Huang, Yijiao Jiang, V. R. Reddy Marthala, Yean Sang Ooi, Jens Weitkamp, Michael Hunger*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

52 Citations (Scopus)

Abstract

1H MAS NMR spectroscopy was applied for a quantitative investigation of the concentration of hydroxyl groups on lanthanum-exchanged zeolites X and Y as a function of the dehydration temperature. A maximum concentration of Brønsted acidic bridging OH groups (SiOHAl) was reached upon dehydration of zeolites La,Na-X and La,Na-Y at 423 K. Further raise of the dehydration temperature leads to the recombination of the above-mentioned hydroxyl groups, while the dealumination of the framework is negligible. The maximum number of bridging OH groups formed on zeolites La,Na-X and La,Na-Y correlates well with the lanthanum exchange degree. By adsorption of deuterated acetonitrile as a probe molecule, an increase of the acid strength of bridging OH groups in lanthanum-exchanged zeolites X and Y was found. This finding is explained by the polarizing effect of multivalent lanthanum cations, which leads to a withdrawal of electrons from the O-H bonds of Brønsted acid sites in lanthanum-exchanged zeolites with a high concentration of these extra-framework cations.

Original languageEnglish
Pages (from-to)129-136
Number of pages8
JournalMicroporous and Mesoporous Materials
Volume104
Issue number1-3
DOIs
Publication statusPublished - 23 Aug 2007
Externally publishedYes

Keywords

  • Acid strength
  • Dehydration
  • Solid-state NMR spectroscopy
  • Thermal stability
  • Zeolites La,Na-X and La,Na-Y

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