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Issue 37, 2010
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A comparative IR characterization of acidic sites on HY zeolite by pyridine and CO probes with silicaalumina and γ-alumina references

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Abstract

Using IR spectroscopy, three different surface states of HY zeolite were probed by successive adsorption of CO at 143 K followed by evacuation and pyridine adsorption at 523 K: HY zeolite [1] without strong Lewis acid sites (LAS); [2] after high temperature (873 K) evacuation to convert Brønsted acid sites (BAS) to strong LAS; and [3] after water re-adsorption on HY zeolite [2] to recover BAS from LAS. The original surface of HY zeolite [1] seemed to be recovered on HY zeolite [3] after high temperature evacuation and water treatment by CO adsorption, while a part of generated LAS on HY zeolite [2] seemed irreversible on HY zeolite [3] to HY zeolite [1] by pyridine adsorption. To clarify this discrepancy, re-examination of the IR spectra of adsorbed CO and pyridine on γ-alumina and silicaalumina after similar treatments to those on HY zeolite was conducted. Based on the results of CO adsorption on γ-alumina and silicaalumina, the presence of extra-framework aluminium sites on HY zeolite [1] was confirmed. High temperature evacuation of HY zeolite [1] formed very strong LAS, a part of which was irreversible to BAS by water re-adsorption at room temperature. The irreversible sites on HY zeolite [3] were assigned to non-acidic OH groups attributed to silicaalumina. The non-acidic OH groups on HY zeolite [3], which were BAS on HY zeolite [1], hydrogen-bonded to pyridine to show IR spectra similar to those adsorbed on LAS. Thus, LAS on HY zeolite [3] seemed irreversible by pyridine adsorption after water re-adsorption. On the other hand, CO adsorbed on non-acidic OH groups showed a band at only slightly lower frequency (2160 cm−1) than that of BAS (2178 cm−1), resulting in overlapps and ignoring their presence. Thus, CO adsorption seemed to show that complete recovery of LAS to BAS occurred.

Graphical abstract: A comparative IR characterization of acidic sites on HY zeolite by pyridine and CO probes with silica–alumina and γ-alumina references

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Publication details

The article was received on 13 Apr 2010, accepted on 14 May 2010 and first published on 03 Aug 2010


Article type: Paper
DOI: 10.1039/C0CP00203H
Citation: Phys. Chem. Chem. Phys., 2010,12, 11576-11586

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    A comparative IR characterization of acidic sites on HY zeolite by pyridine and CO probes with silicaalumina and γ-alumina references

    J. N. Kondo, R. Nishitani, E. Yoda, T. Yokoi, T. Tatsumi and K. Domen, Phys. Chem. Chem. Phys., 2010, 12, 11576
    DOI: 10.1039/C0CP00203H

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