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

Research output: Contribution to journalArticle

7 Citations (Scopus)

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
Externally publishedYes

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interfacial energy
Platelets
Transmission electron microscopy
platelets
Interfacial energy
catalysts
transmission electron microscopy
Catalysts
Free energy
free energy
Imaging techniques
Crystallite size
Electron diffraction
Energy dispersive spectroscopy
flat surfaces
electron diffraction
Single crystals
expansion
single crystals
products

ASJC Scopus subject areas

  • Physical and Theoretical 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

Morphological evolution of Ba(NO3)2 supported on α-Al2O3(0001) : An in situ TEM study. / Wang, C. M.; Kwak, J. H.; Kim, D. H.; Szanyi, J.; Sharma, R.; Thevuthasan, S.; Peden, C. H F.

In: Journal of Physical Chemistry B, Vol. 110, No. 24, 22.06.2006, p. 11878-11883.

Research output: Contribution to journalArticle

Wang, CM, Kwak, JH, Kim, DH, Szanyi, J, Sharma, R, Thevuthasan, S & Peden, CHF 2006, 'Morphological evolution of Ba(NO3)2 supported on α-Al2O3(0001): An in situ TEM study', Journal of Physical Chemistry B, vol. 110, no. 24, pp. 11878-11883. https://doi.org/10.1021/jp060235i
Wang CM, Kwak JH, Kim DH, Szanyi J, Sharma R, Thevuthasan S et al. Morphological evolution of Ba(NO3)2 supported on α-Al2O3(0001): An in situ TEM study. Journal of Physical Chemistry B. 2006 Jun 22;110(24):11878-11883. https://doi.org/10.1021/jp060235i
Wang, C. M. ; Kwak, J. H. ; Kim, D. H. ; Szanyi, J. ; Sharma, R. ; Thevuthasan, S. ; Peden, C. H F. / Morphological evolution of Ba(NO3)2 supported on α-Al2O3(0001) : An in situ TEM study. In: Journal of Physical Chemistry B. 2006 ; Vol. 110, No. 24. pp. 11878-11883.
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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.",
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