Activation conditions play a key role in the activity of zeolite CaY: NMR and product studies of Brønsted acidity

Hsien Ming Kao, Clare P. Grey, Kasi Pitchumani, P. H. Lakshminarasimhan, Vaidhyanathan Ramamurthy

Research output: Contribution to journalArticle

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Abstract

CaY, activated under different conditions, was characterized with 1H, 31P, and 1H/27A] double resonance MAS NMR. The 1H MAS NMR spectra of CaY, calcined in an oven at 500 °C, shows resonances from H2O (bound to Ca2+ and the zeolite framework), CaOH+, aluminum hydroxides, silanols, and Brønsted acid sites. No evidence for Lewis acidity is observed on adsorption of trimethylphosphine, and an estimate of ≈16 Brønsted acid sites per unit cell is obtained for this sample. CaY activated in an oven at higher temperatures contains less water, but all the other species are still present. In contrast, CaY activated by slow ramping of the temperature under vacuum to 500 or 600 °C shows a much lower concentration of Brønsted acid sites (<1/unit cell). Again, no evidence for Lewis acidity was observed. These NMR results have been utilized to understand the very different product distributions that are observed for reactions of 1,1- and 1,2-diarylethylenes in zeolite CaY activated in an oven (in air) and under vacuum. Samples with high concentrations of Brønsted acid sites react stoichiometrically with these sites, yielding diarylalkanes. At low concentrations, the Brønsted acid sites can act catalytically resulting in isomerization reactions.

Original languageEnglish
Pages (from-to)5627-5638
Number of pages12
JournalJournal of Physical Chemistry A
Volume102
Issue number28
StatePublished - Jul 9 1998
Externally publishedYes

Fingerprint

Zeolites
Acidity
acidity
Chemical activation
Nuclear magnetic resonance
activation
ovens
Ovens
nuclear magnetic resonance
acids
Acids
products
low concentrations
Vacuum
Aluminum Hydroxide
vacuum
Isomerization
cells
isomerization
hydroxides

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Activation conditions play a key role in the activity of zeolite CaY : NMR and product studies of Brønsted acidity. / Kao, Hsien Ming; Grey, Clare P.; Pitchumani, Kasi; Lakshminarasimhan, P. H.; Ramamurthy, Vaidhyanathan.

In: Journal of Physical Chemistry A, Vol. 102, No. 28, 09.07.1998, p. 5627-5638.

Research output: Contribution to journalArticle

Kao, Hsien Ming ; Grey, Clare P. ; Pitchumani, Kasi ; Lakshminarasimhan, P. H. ; Ramamurthy, Vaidhyanathan. / Activation conditions play a key role in the activity of zeolite CaY : NMR and product studies of Brønsted acidity. In: Journal of Physical Chemistry A. 1998 ; Vol. 102, No. 28. pp. 5627-5638.
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