Characterization and acidic properties of aluminum-exchanged zeolites X and Y

Jun Huang, Yijiao Jiang, V. R Reddy Marthala, Bejoy Thomas, Ekaterina Romanova, Michael Hunger*

*Corresponding author for this work

Research output: Contribution to journalArticle

68 Citations (Scopus)

Abstract

Zeolites Al,Na - X and Al, Na - Y with defined numbers of extraframework aluminum cations were prepared by exchange in an aqueous solution of aluminum nitrate. A maximum concentration of Brønsted acidic bridging OH groups in supercages (SiOHsupAl) was reached upon dehydration of zeolites Al,Na-X and Al,Na-Y at 423 K. Further raising of the dehydration temperature led to a dehydroxylation of zeolites due to the recombination of aluminum hydroxyl groups with hydroxyl protons of bridging OH groups. High-field 27Al multiple-quantum magic-angle spinning (MQMAS) NMR spectroscopy was utilized to study zeolites Al,Na-X/61 and Al,Na-Y/63 dehydrated at 423 K. Second-order quadrupolar effect parameters of 10.1 - 11.0 MHz for tetrahedrally coordinated framework aluminum atoms, compensated in their negative charge by hydroxyl protons (AlIV/H+) and aluminum cations (Al IV/Alx+), 3.6-4.4 MHz for tetrahedrally coordinated framework aluminum atoms compensated by sodium cations (AIIV/Na +), and 5.6-7.6 MHz for pentacoordinated extraframework aluminum cations (Alx+ cat.) were obtained. Comparison of the number of AlOH groups with the number of pentacoordinated extraframework aluminum cations determined by one-dimensional high-field 27Al MAS NMR spectroscopy gave a ratio near 1:1. This finding and the five-fold coordination of the cationic extraframework aluminum species hint to the presence of HO-Al +-O-Al+-OH compounds, but also a minor number of Al(OH)2+ and AlO+ species could exist. The enhanced acid strength of bridging OH groups in zeolites Al,Na-X and Al,Na-Y in comparison with zeolites H,Na-X and H,Na-Y, as found by adsorption of acetonitrile, may be due to a polarizing effect of cationic extraframework aluminum species in the vicinity of Brønsted acid sites.

Original languageEnglish
Pages (from-to)3811-3818
Number of pages8
JournalJournal of Physical Chemistry C
Volume112
Issue number10
DOIs
Publication statusPublished - 13 Mar 2008
Externally publishedYes

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    Huang, J., Jiang, Y., Marthala, V. R. R., Thomas, B., Romanova, E., & Hunger, M. (2008). Characterization and acidic properties of aluminum-exchanged zeolites X and Y. Journal of Physical Chemistry C, 112(10), 3811-3818. https://doi.org/10.1021/jp7103616