Morphological evolution of Ba(NO3)2 supported on α-Al2O3(0001): An in situ TEM study

C. M. Wang, J. H. Kwak, D. H. Kim, J. Szanyi, R. Sharma, S. Thevuthasan, C. H.F. Peden

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    Abstract

    A key question for the BaO-based NOx storage/reduction catalyst system is the morphological evolution of the catalyst particles during the uptake and release of NOx. Notably, because the formed product during NOx uptake, Ba(NO3)2, requires a lattice expansion from BaO, one can anticipate that significant structural rearrangements are possible during the storage/reduction processes. Associated with the small crystallite size of high-surface area γ-Al2O3, it is difficult to extract structural and morphological features of Ba(NO3)2 supported on γ-Al2O3 by any direct imaging method, including transmission electron microscopy. In this work, by choosing a model system of Ba(NO3)2 particles supported on single-crystal α-Al2O3, we have investigated the structural and morphological features of Ba(NO3)2 as well as the formation of BaO from Ba(NO3)2 during the thermal release of NOx, using ex-situ and in-situ TEM imaging, electron diffraction, energy dispersive spectroscopy (EDS), and Wulff shape construction. We find that Ba(NO3)2 supported on α-Al2O3 possesses a platelet morphology, with the interface and facets being invariably the eight {111} planes. Formation of the platelet structure leads to an enlarged interface area between Ba(NO3)2 and α-Al 2O3, indicating that the interfacial energy is lower than the Ba(NO3)2 surface free energy. In fact, Wulff shape constructions indicate that the interfacial energy is ∼ 1/4 of the {111} surface free energy of Ba(NO3)2. The orientation relationship between Ba(NO3)2 and the α-Al 2O3 is α-Al2O3[0001]// Ba(NO3)2[111] and α-Al2O 3(1-210)//Ba-(NO3)2(110). Thus, the results clearly demonstrate dramatic morphology changes in these materials during NOx release processes. Such changes are expected to have significant consequences for the operation of the practical NOx storage/reduction catalyst technology.

    Original languageEnglish
    Pages (from-to)11878-11883
    Number of pages6
    JournalJournal of Physical Chemistry B
    Volume110
    Issue number24
    DOIs
    Publication statusPublished - 22 Jun 2006

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    ASJC Scopus subject areas

    • Physical and Theoretical Chemistry
    • Surfaces, Coatings and Films
    • Materials Chemistry

    Cite this

    Wang, C. M., Kwak, J. H., Kim, D. H., Szanyi, J., Sharma, R., Thevuthasan, S., & Peden, C. H. F. (2006). Morphological evolution of Ba(NO3)2 supported on α-Al2O3(0001): An in situ TEM study. Journal of Physical Chemistry B, 110(24), 11878-11883. https://doi.org/10.1021/jp060235i