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

Ja Hun Kwak, Donghai Mei, Cheol Woo Yi, Do Heui Kim, Charles H.F. Peden, Lawrence F. Allard, János Szanyi

Research output: Contribution to journalArticlepeer-review

81 Scopus citations

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.".

Original languageEnglish
Pages (from-to)17-22
Number of pages6
JournalJournal of Catalysis
Volume261
Issue number1
DOIs
StatePublished - Jan 1 2009

Funding

We gratefully acknowledge the US Department of Energy (DOE), Office of Basic Energy Sciences, Division of Chemical Sciences for the support of this work. The research described in this paper was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle Memorial Institute under contract number DE-AC05-76RL01830. This work also supported by the LDRD project of Catalysis Initiative at PNNL. The computing time was granted by National Energy Research Scientific Center (NERSC). We also acknowledge the High Temperature Materials Laboratory at ORNL where the HR-STEM images were acquired.

Keywords

  • BaO/γ-AlO
  • Density Functional Theory
  • FTIR
  • HR-STEM
  • NO storage

Fingerprint

Dive into the research topics of 'Understanding the nature of surface nitrates in BaO/γ-Al2O3 NOx storage materials: A combined experimental and theoretical study'. Together they form a unique fingerprint.

Cite this