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Changing morphology of BaO/Al2O3 during NO2 uptake and release.
Janos Szanyi1, Ja Hun Kwak, Jonathan Hanson
1Interfacial Chemistry and Engineering, Chemical Sciences Division and Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
The Journal of Physical Chemistry. B
|July 21, 2006
Summary
Barium oxide (BaO) catalysts for nitrogen oxide (NOx) storage and reduction undergo dynamic morphological changes. These transformations, involving barium nitrate (Ba(NO3)2) and BaO phases, are crucial for understanding catalyst performance.
Area of Science:
- Catalysis science
- Materials science
- Surface chemistry
Background:
- Barium oxide-based materials are critical for NOx storage and reduction catalysts.
- Understanding the dynamic behavior of these catalysts under operating conditions is essential for improving their efficiency.
Purpose of the Study:
- To investigate the morphological evolution of Ba-oxide-based NOx storage/reduction catalysts.
- To elucidate the dynamic changes in Ba-containing phases during the NOx storage and reduction process.
Main Methods:
- Time-resolved X-ray diffraction
- Transmission electron microscopy
- Energy dispersed spectroscopy
Main Results:
- Formation of large Ba(NO3)2 crystallites during preparation.
- Decomposition to BaO monolayer and nanocrystalline particles upon heating.
- Reformation of Ba(NO3)2 upon NO2 exposure, with smaller average crystal size than initially prepared.
- Evidence for both monolayer and crystalline Ba(NO3)2 phases after NO2 treatment.
Conclusions:
- Ba-containing phases in NOx storage/reduction catalysts exhibit dynamic morphological changes.
- A proposed morphology cycle involving BaO and Ba(NO3)2 phases.
- These dynamic changes are key to understanding catalyst performance variations.