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Title: Water-induced Morphology Changes in BaO/g-Al2O3 Nox Storage Materials

Abstract

Exposure of NO{sub 2}-saturated BaO/{gamma}-Al{sub 2}O{sub 3} NO{sub x} storage materials to H{sub 2}O vapor results in the conversion of surface nitrates to Ba(NO{sub 3}){sub 2} crystallites, causing dramatic morphological changes in the Ba-containing phase, demonstrating a role for water in affecting the NO{sub x} storage/reduction properties of these materials.

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930640
Report Number(s):
BNL-81051-2008-JA
TRN: US200901%%8
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Chemical Communications; Journal Volume: 2007
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 54 ENVIRONMENTAL SCIENCES; MORPHOLOGICAL CHANGES; BARIUM OXIDES; ALUMINIUM OXIDES; NITROGEN OXIDES; SORPTION; ADSORBENTS; national synchrotron light source

Citation Formats

Szanyi,J., Kwak, J., Kim, D., Wang, X., Hanson, J., Chimentao, R., and Peden, C. Water-induced Morphology Changes in BaO/g-Al2O3 Nox Storage Materials. United States: N. p., 2007. Web. doi:10.1039/b613674e.
Szanyi,J., Kwak, J., Kim, D., Wang, X., Hanson, J., Chimentao, R., & Peden, C. Water-induced Morphology Changes in BaO/g-Al2O3 Nox Storage Materials. United States. doi:10.1039/b613674e.
Szanyi,J., Kwak, J., Kim, D., Wang, X., Hanson, J., Chimentao, R., and Peden, C. Mon . "Water-induced Morphology Changes in BaO/g-Al2O3 Nox Storage Materials". United States. doi:10.1039/b613674e.
@article{osti_930640,
title = {Water-induced Morphology Changes in BaO/g-Al2O3 Nox Storage Materials},
author = {Szanyi,J. and Kwak, J. and Kim, D. and Wang, X. and Hanson, J. and Chimentao, R. and Peden, C.},
abstractNote = {Exposure of NO{sub 2}-saturated BaO/{gamma}-Al{sub 2}O{sub 3} NO{sub x} storage materials to H{sub 2}O vapor results in the conversion of surface nitrates to Ba(NO{sub 3}){sub 2} crystallites, causing dramatic morphological changes in the Ba-containing phase, demonstrating a role for water in affecting the NO{sub x} storage/reduction properties of these materials.},
doi = {10.1039/b613674e},
journal = {Chemical Communications},
number = ,
volume = 2007,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • The effect of water on the morphology of BaO/Al2O3-based NOx storage materials was investigated using Fourier transform infrared spectroscopy, temperature programmed desorption, and time-resolved synchrotron X-ray diffraction techniques. The results of this multi-spectroscopy study reveal that, in the presence of water, surface Ba-nitrates convert to bulk nitrates, and water facilitates the formation of large Ba(NO3)2 particles. This process is completely reversible, i.e. after the removal of water from the storage material a significant fraction of the bulk nitrates re-convert to surface nitrates. NO2 exposure of a H2O-containing (wet) BaO/Al2O3 sample results in the formation of nitrites and bulk nitrates exclusively,more » i.e. no surface nitrates form. After further exposure to NO2, the nitrites completely convert to bulk nitrates. The amount of NOx taken up by the storage material is, however, essentially unaffected by the presence of water, regardless of whether the water was dosed prior to or after NO2 exposure. Based on the results of this study we are now able to explain most of the observations reported in the literature on the effect of water on NOx uptake on similar storage materials.« less
  • Exposure of NO2-saturated BaO/γ-Al2O3 NOx storage materials to H2O vapour results in the conversion of surface nitrates to Ba(NO3)2 crystallites, causing dramatic morphological changes in the Ba-containing phase, demonstrating a role for water in affecting the NOx storage/reduction properties of these materials.
  • The effect of water on the morphology of BaO/Al{sub 2}O{sub 3}-based NO{sub x} storage materials was investigated using Fourier transform infrared spectroscopy, temperature programmed desorption, and time-resolved synchrotron X-ray diffraction techniques. The results of this multispectroscopy study reveal that in the presence of water surface Ba-nitrates convert to bulk nitrates and water facilitates the formation of large Ba(NO{sub 3}){sub 2} particles. The conversion of surface to bulk Ba-nitrates is completely reversible (i.e., after the removal of water from the storage material a significant fraction of the bulk nitrates reconverts to surface nitrates). NO{sub 2} exposure of a H{sub 2}O-containing (wet)more » BaO/Al{sub 2}O{sub 3} sample results in the formation of nitrites and bulk nitrates exclusively (i.e., no surface nitrates form). After further exposure to NO{sub 2}, the nitrites completely convert to bulk nitrates. The amount of NO{sub x} taken up by the storage material, however, is essentially unaffected by the presence of water regardless of whether the water was dosed prior to or after NO{sub 2} exposure. On the basis of the results of this study, we are now able to explain most of the observations reported in the literature on the effect of water on NO{sub x} uptake on similar storage materials.« less
  • The special role of the interface between the active catalytic phase (metal or metal oxide) and the oxide support in determining the properties of practical catalysts has long been recognized; however, it is still very poorly understood in most systems
  • Relationship between Pt particle size and NOx storage performance was investigated over a model Pt/BaO/Al2O3 and an enhanced lean NOx trap catalyst (LNT). These catalysts were treated at elevated temperature to mimic the effect of thermal aging encountered during the desulfation step in NOx trap catalyst regeneration. Combination of in situ time-resolved X-ray Diffraction (TR-XRD), DRIFT measurement after CO adsorption and TEM observation over the thermally aged samples clearly shows the sintering behavior of Pt crystalline as a function of time and temperature. Under elevated temperatures, the crystalline growth of Pt occurs within a short time (e.g. 1.5 hr) followedmore » by the gradual increase with time. NOx storage reaction performed after successive thermal treatments of catalyst under oxygen and in situ XRD experiment have allowed us to correlate the NOx storage performance with phase change. Comparing the simple Pt-BaO/Al2O3 sample with the enhanced one which shows much less Pt sintering, it was confirmed that the Pt crystalline size plays a critical role in determining the NOx storage activity, in other words, the retention of the small Pt particles after thermal aging is crucial to maintain a higher activity. In conclusion, the prevention of Pt sintering when operated at elevated temperature must be a key factor to design the more durable LNT catalyst, thus potentially implying the practical importance for the improvement of the LNT technology.« less