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Title: Reduction of Stored NOx on Pt/Al₂O₃ and Pt/BaO/Al₂O₃ Catalysts with H₂ and CO

Abstract

In situ FTIR spectroscopy coupled with mass spectrometry, and time resolved X-ray diffraction were used to study the efficiency of nitrate reduction with CO and H₂ on Pt/Al₂O₃ and Pt/BaO/Al₂O₃ NOx storage-reduction (NSR) catalysts. Surface nitrates were generated by NO₂ adsorption and their reduction efficiencies were examined on the catalysts together with the analysis of the gas phase composition in the presence of the two different reductants. H₂ was found to be a more effective reducing agent than CO. In particular, the reduction of surface nitrates proceeds very efficiently with H₂ even at low temperatures (~420 K). During reduction with CO, isocyanates were observed to form on every catalyst component. These surface isocyanates, however, readily react with water to form CO₂ and ammonia. The thus formed NH₃, in turn, reacts with stored NOx at higher temperatures (>473K) to produce N₂. In the absence of H₂O, the NCO species are stable to high temperatures, and removed only from the catalyst when they react with NOx thermal decomposition products to form N₂ and CO₂. The results of this study point to a complex reaction mechanism that involves the removal of surface oxygen atoms from the Pt particles by either H₂ or CO,more » the direct reduction of stored NOx with H₂ (low temperature NOx reduction), the formation and the subsequent hydrolysis of NCO species, as well as the direct reaction of NCO with decomposing NOx (high temperature NOx reduction).« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
882956
Report Number(s):
PNNL-SA-46078
6695; VT0401000; TRN: US200621%%873
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Catalysis, 239(1):51-64
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; ADSORPTION; AMMONIA; ATOMS; CATALYSTS; DIRECT REACTIONS; EFFICIENCY; HYDROLYSIS; ISOCYANATES; MASS SPECTROSCOPY; NITRATES; OXYGEN; PYROLYSIS; REACTION KINETICS; REDUCING AGENTS; REMOVAL; SPECTROSCOPY; WATER; X-RAY DIFFRACTION; NOx reduction; Reduction efficiency; Pt/Al2O3; Pt/BaO/Al2O3; FTIR; TR-XRD; Environmental Molecular Sciences Laboratory

Citation Formats

Szailer, Tamas, Kwak, Ja Hun, Kim, Do Heui, Hanson, Jonathan, Peden, Charles HF, and Szanyi, Janos. Reduction of Stored NOx on Pt/Al₂O₃ and Pt/BaO/Al₂O₃ Catalysts with H₂ and CO. United States: N. p., 2006. Web. doi:10.1016/j.jcat.2006.01.014.
Szailer, Tamas, Kwak, Ja Hun, Kim, Do Heui, Hanson, Jonathan, Peden, Charles HF, & Szanyi, Janos. Reduction of Stored NOx on Pt/Al₂O₃ and Pt/BaO/Al₂O₃ Catalysts with H₂ and CO. United States. doi:10.1016/j.jcat.2006.01.014.
Szailer, Tamas, Kwak, Ja Hun, Kim, Do Heui, Hanson, Jonathan, Peden, Charles HF, and Szanyi, Janos. Sat . "Reduction of Stored NOx on Pt/Al₂O₃ and Pt/BaO/Al₂O₃ Catalysts with H₂ and CO". United States. doi:10.1016/j.jcat.2006.01.014.
@article{osti_882956,
title = {Reduction of Stored NOx on Pt/Al₂O₃ and Pt/BaO/Al₂O₃ Catalysts with H₂ and CO},
author = {Szailer, Tamas and Kwak, Ja Hun and Kim, Do Heui and Hanson, Jonathan and Peden, Charles HF and Szanyi, Janos},
abstractNote = {In situ FTIR spectroscopy coupled with mass spectrometry, and time resolved X-ray diffraction were used to study the efficiency of nitrate reduction with CO and H₂ on Pt/Al₂O₃ and Pt/BaO/Al₂O₃ NOx storage-reduction (NSR) catalysts. Surface nitrates were generated by NO₂ adsorption and their reduction efficiencies were examined on the catalysts together with the analysis of the gas phase composition in the presence of the two different reductants. H₂ was found to be a more effective reducing agent than CO. In particular, the reduction of surface nitrates proceeds very efficiently with H₂ even at low temperatures (~420 K). During reduction with CO, isocyanates were observed to form on every catalyst component. These surface isocyanates, however, readily react with water to form CO₂ and ammonia. The thus formed NH₃, in turn, reacts with stored NOx at higher temperatures (>473K) to produce N₂. In the absence of H₂O, the NCO species are stable to high temperatures, and removed only from the catalyst when they react with NOx thermal decomposition products to form N₂ and CO₂. The results of this study point to a complex reaction mechanism that involves the removal of surface oxygen atoms from the Pt particles by either H₂ or CO, the direct reduction of stored NOx with H₂ (low temperature NOx reduction), the formation and the subsequent hydrolysis of NCO species, as well as the direct reaction of NCO with decomposing NOx (high temperature NOx reduction).},
doi = {10.1016/j.jcat.2006.01.014},
journal = {Journal of Catalysis, 239(1):51-64},
number = ,
volume = ,
place = {United States},
year = {Sat Apr 01 00:00:00 EST 2006},
month = {Sat Apr 01 00:00:00 EST 2006}
}
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