Al2O3-based passive NOx adsorbers for low temperature applications

Yaying Ji; Shuli Bai; Mark Crocker

doi:10.1016/j.apcatb.2015.01.025

Al₂O₃-based passive NOx adsorbers for low temperature applications

Yaying Ji, Shuli Bai, Mark Crocker

Chemistry

Research output: Contribution to journal › Article › peer-review

138 Scopus citations

Abstract

NOx storage on Pt/Al₂O₃ and Pt/La-Al₂O₃ in the temperature range 80-160°C was investigated by means of microreactor and in situ DRIFTS experiments, to ascertain their suitability for passive NOx adsorber applications. Addition of 1wt% La to Al₂O₃ resulted in the creation of new NOx storage sites and improved NOx storage efficiency. However, according to TPD measurements, Pt/La-Al₂O₃ exhibited slightly lower NOx desorption efficiency below 250°C than Pt/Al₂O₃. During repeated NOx adsorption-desorption cycles, almost no benefit of La addition was observed after five cycles, due to the inability to regenerate the strong NOx storage sites associated with the La at 250°C. DRIFTS measurements indicated that during NOx-TPD, nitrites and weakly bound nitrate species were initially removed from the surface of Pt/Al₂O₃ and Pt/La-Al₂O₃. NOx desorption at higher temperatures (>250°C) was mainly associated with nitrate decomposition. DRIFTS measurements on Pt/Al₂O₃ revealed that NOx was mainly stored on the Al₂O₃ surface when oxidized Pt was present, although when a reductive re-treatment was applied NOx storage on reduced Pt sites became significant and total NOx storage efficiency was improved. However, compared to bare Al₂O₃, NOx desorption efficiency below 250°C significantly dropped when Pt was present, and was even lower after pre-reduction in H₂. Overall, the Pt-Al without pre-reduction showed the highest amount of NOx desorption below 250°C.

Original language	English
Pages (from-to)	283-292
Number of pages	10
Journal	Applied Catalysis B: Environmental
Volume	170-171
DOIs	https://doi.org/10.1016/j.apcatb.2015.01.025
State	Published - Jul 1 2015

Bibliographical note

Publisher Copyright:
© 2015 Elsevier B.V.

Funding

The authors thank Dr. Dali Qian and Shelley Hopps for XPS and XRD measurements, respectively, as well as Drs. Christine Lambert and Joe Theis of Ford Motor Co. for helpful discussions. Sasol is thanked for a gift of γ-Al 2 O 3 . This project was funded by the National Science Foundation and the U.S. Department of Energy (DOE) under award no. CBET-1258742 . However, any opinions, findings, conclusions, or recommendations expressed herein are those of the authors and do not necessarily reflect the views of the DOE.

Funders	Funder number
U.S. Department of Energy Chinese Academy of Sciences Guangzhou Municipal Science and Technology Project Oak Ridge National Laboratory Extreme Science and Engineering Discovery Environment National Science Foundation National Energy Research Scientific Computing Center National Natural Science Foundation of China
U.S. Department of Energy Oak Ridge National Laboratory U.S. Department of Energy National Science Foundation National Energy Research Scientific Computing Center	CBET-1258742
U.S. Department of Energy Oak Ridge National Laboratory U.S. Department of Energy National Science Foundation National Energy Research Scientific Computing Center

Keywords

Adsorption
Alumina
Desorption
Lanthanum
Low temperature
Passive nox adsorber

ASJC Scopus subject areas

Catalysis
General Environmental Science
Process Chemistry and Technology

Access to Document

10.1016/j.apcatb.2015.01.025

Cite this

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title = "Al2O3-based passive NOx adsorbers for low temperature applications",

abstract = "NOx storage on Pt/Al2O3 and Pt/La-Al2O3 in the temperature range 80-160°C was investigated by means of microreactor and in situ DRIFTS experiments, to ascertain their suitability for passive NOx adsorber applications. Addition of 1wt\% La to Al2O3 resulted in the creation of new NOx storage sites and improved NOx storage efficiency. However, according to TPD measurements, Pt/La-Al2O3 exhibited slightly lower NOx desorption efficiency below 250°C than Pt/Al2O3. During repeated NOx adsorption-desorption cycles, almost no benefit of La addition was observed after five cycles, due to the inability to regenerate the strong NOx storage sites associated with the La at 250°C. DRIFTS measurements indicated that during NOx-TPD, nitrites and weakly bound nitrate species were initially removed from the surface of Pt/Al2O3 and Pt/La-Al2O3. NOx desorption at higher temperatures (>250°C) was mainly associated with nitrate decomposition. DRIFTS measurements on Pt/Al2O3 revealed that NOx was mainly stored on the Al2O3 surface when oxidized Pt was present, although when a reductive re-treatment was applied NOx storage on reduced Pt sites became significant and total NOx storage efficiency was improved. However, compared to bare Al2O3, NOx desorption efficiency below 250°C significantly dropped when Pt was present, and was even lower after pre-reduction in H2. Overall, the Pt-Al without pre-reduction showed the highest amount of NOx desorption below 250°C.",

keywords = "Adsorption, Alumina, Desorption, Lanthanum, Low temperature, Passive nox adsorber",

author = "Yaying Ji and Shuli Bai and Mark Crocker",

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year = "2015",

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doi = "10.1016/j.apcatb.2015.01.025",

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AU - Ji, Yaying

AU - Bai, Shuli

AU - Crocker, Mark

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N2 - NOx storage on Pt/Al2O3 and Pt/La-Al2O3 in the temperature range 80-160°C was investigated by means of microreactor and in situ DRIFTS experiments, to ascertain their suitability for passive NOx adsorber applications. Addition of 1wt% La to Al2O3 resulted in the creation of new NOx storage sites and improved NOx storage efficiency. However, according to TPD measurements, Pt/La-Al2O3 exhibited slightly lower NOx desorption efficiency below 250°C than Pt/Al2O3. During repeated NOx adsorption-desorption cycles, almost no benefit of La addition was observed after five cycles, due to the inability to regenerate the strong NOx storage sites associated with the La at 250°C. DRIFTS measurements indicated that during NOx-TPD, nitrites and weakly bound nitrate species were initially removed from the surface of Pt/Al2O3 and Pt/La-Al2O3. NOx desorption at higher temperatures (>250°C) was mainly associated with nitrate decomposition. DRIFTS measurements on Pt/Al2O3 revealed that NOx was mainly stored on the Al2O3 surface when oxidized Pt was present, although when a reductive re-treatment was applied NOx storage on reduced Pt sites became significant and total NOx storage efficiency was improved. However, compared to bare Al2O3, NOx desorption efficiency below 250°C significantly dropped when Pt was present, and was even lower after pre-reduction in H2. Overall, the Pt-Al without pre-reduction showed the highest amount of NOx desorption below 250°C.

AB - NOx storage on Pt/Al2O3 and Pt/La-Al2O3 in the temperature range 80-160°C was investigated by means of microreactor and in situ DRIFTS experiments, to ascertain their suitability for passive NOx adsorber applications. Addition of 1wt% La to Al2O3 resulted in the creation of new NOx storage sites and improved NOx storage efficiency. However, according to TPD measurements, Pt/La-Al2O3 exhibited slightly lower NOx desorption efficiency below 250°C than Pt/Al2O3. During repeated NOx adsorption-desorption cycles, almost no benefit of La addition was observed after five cycles, due to the inability to regenerate the strong NOx storage sites associated with the La at 250°C. DRIFTS measurements indicated that during NOx-TPD, nitrites and weakly bound nitrate species were initially removed from the surface of Pt/Al2O3 and Pt/La-Al2O3. NOx desorption at higher temperatures (>250°C) was mainly associated with nitrate decomposition. DRIFTS measurements on Pt/Al2O3 revealed that NOx was mainly stored on the Al2O3 surface when oxidized Pt was present, although when a reductive re-treatment was applied NOx storage on reduced Pt sites became significant and total NOx storage efficiency was improved. However, compared to bare Al2O3, NOx desorption efficiency below 250°C significantly dropped when Pt was present, and was even lower after pre-reduction in H2. Overall, the Pt-Al without pre-reduction showed the highest amount of NOx desorption below 250°C.

KW - Adsorption

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