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Understanding the nature of surface nitrates in BaO/γ -Al2O3 NOx storage materials: A combined experimental and theoretical study

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Abstract.
A combined experimental-theory approach was applied to unambiguously determine the nature of
“surface nitrates” in BaO/γ -Al2O3 NOx storage materials. High resolution scanning transmission electron
microscopy images reveal that at a low BaO coverage of 2 wt% on γ -Al2O3 monomeric BaO units are
present almost exclusively. These molecularly dispersed BaO units are concentrated on the (100) facets
of the alumina crystallites, while other facets remain practically BaO-free The results of the density
functional theory calculations predicted adsorption geometries for the (BaO)x (x = 1 and 2) units. The
energetically most favorable BaO monomer and dimer units anchor to pentacoordinate Al3+ sites on the
(100) facets of γ -Al2O3 in such geometries that maximize their interactions with the support surface.
The calculated vibrational frequencies of the energetically most favorable nitrate species formed upon
the interaction of NO2 with the monomeric and dimeric BaO units agree remarkably well with those
observed experimentally by infrared spectroscopy and identified as “surface nitrates.”

Keywords:
BaO/γ -Al2O3
NOx storage
HR-STEM
FTIR
Density Functional Theory

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Informasi Detail

Judul Seri

Journal of Catalysis

No. Panggil

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Penerbit

London : Elsevier Inc.., 2009

Deskripsi Fisik

Journal of Catalysis 261 (2009) 17–22

Bahasa

English

ISBN/ISSN

00219517

Klasifikasi

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Tipe Isi

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Tipe Media

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Tipe Pembawa

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Edisi

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Subjek

KIMIA

Info Detail Spesifik

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Pernyataan Tanggungjawab

agus

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