Reduction over zeolite-based catalysts of nitrogen oxides in emissions containing excess oxygen: Unraveling the reaction mechanism

Hai Ying Chen; Qi Sun; Bin Wen; Young Hoon Yeom; Eric Weitz; Wolfgang M.H. Sachtler

doi:10.1016/j.cattod.2004.05.002

Reduction over zeolite-based catalysts of nitrogen oxides in emissions containing excess oxygen: Unraveling the reaction mechanism

Hai Ying Chen, Qi Sun, Bin Wen, Young Hoon Yeom, Eric Weitz, Wolfgang M.H. Sachtler

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56 Scopus citations

Abstract

Reduction of NO_x to N₂ over zeolite-based catalysts is a multi-step reaction for which transition metal (TM) ions are helpful but not indispensable. The present state of understanding the mechanism is reviewed for the catalyzed NO_x reduction with ammonia or alkanes; reduction with acetaldehyde is also sketched, but will be described in detail in a separate paper. A decisive step is the interaction of two reaction intermediates containing N atoms in different oxidation states. A favorable reaction path uses an organic molecule to reduce part of the NO_x to ammonia, this product then reacts with NO + NO₂ to give N ₂. Isotopic labeling shows that each N₂ molecule has one N atom from the NH₃ intermediate, the other from NO_x. N₂ is formed at room temperature, if an 1:1 mixture of NO and NO ₂ is in contact with an Fe/MFI catalyst covered with NH₃. During NO_x reduction with CH₄ over Pd/zeolite catalysts, H/D exchange of methane has been observed, indicating that methane is dissociatively adsorbed on Pd⁰ clusters that are present in the steady-state of surface oxidation and reduction steps. BaNaY catalysts, containing negligible impurities of TM elements, catalyze NO_x reduction with acetaldehyde at 200°C. In the prevailing mechanism acetaldehyde is transformed via acetate ions and nitromethane to isocyanic acid, which is hydrolyzed to NH₃. Again, N₂ is ultimately produced from NH₃ and N₂O₃ via ammonium nitrite.

Original language	English
Pages (from-to)	1-10
Number of pages	10
Journal	Catalysis Today
Volume	96
Issue number	1-2
DOIs	https://doi.org/10.1016/j.cattod.2004.05.002
State	Published - 2004
Externally published	Yes

Funding

This work was supported by EMSI Program of the National Science Foundation and the US Department of Energy Office of Science (CHE-9810378) at the Institute for Environmental Catalysis, Northwestern University. Financial aid from the Director of the Chemistry Division, Basic Energy Sciences, US Department of Energy, grant DE-FGO2-87ER13654, is gratefully acknowledged.

Funders	Funder number
National Science Foundation
U.S. Department of Energy	DE-FGO2-87ER13654, CHE-9810378
Basic Energy Sciences
Northwestern University

Keywords

Reduction
Transition metal ions
Zeolite-based catalysts

Access to Document

10.1016/j.cattod.2004.05.002

Cite this

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title = "Reduction over zeolite-based catalysts of nitrogen oxides in emissions containing excess oxygen: Unraveling the reaction mechanism",

abstract = "Reduction of NOx to N2 over zeolite-based catalysts is a multi-step reaction for which transition metal (TM) ions are helpful but not indispensable. The present state of understanding the mechanism is reviewed for the catalyzed NOx reduction with ammonia or alkanes; reduction with acetaldehyde is also sketched, but will be described in detail in a separate paper. A decisive step is the interaction of two reaction intermediates containing N atoms in different oxidation states. A favorable reaction path uses an organic molecule to reduce part of the NOx to ammonia, this product then reacts with NO + NO2 to give N 2. Isotopic labeling shows that each N2 molecule has one N atom from the NH3 intermediate, the other from NOx. N2 is formed at room temperature, if an 1:1 mixture of NO and NO 2 is in contact with an Fe/MFI catalyst covered with NH3. During NOx reduction with CH4 over Pd/zeolite catalysts, H/D exchange of methane has been observed, indicating that methane is dissociatively adsorbed on Pd0 clusters that are present in the steady-state of surface oxidation and reduction steps. BaNaY catalysts, containing negligible impurities of TM elements, catalyze NOx reduction with acetaldehyde at 200°C. In the prevailing mechanism acetaldehyde is transformed via acetate ions and nitromethane to isocyanic acid, which is hydrolyzed to NH3. Again, N2 is ultimately produced from NH3 and N2O3 via ammonium nitrite.",

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author = "Chen, {Hai Ying} and Qi Sun and Bin Wen and Yeom, {Young Hoon} and Eric Weitz and Sachtler, {Wolfgang M.H.}",

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T2 - Unraveling the reaction mechanism

AU - Chen, Hai Ying

AU - Sun, Qi

AU - Wen, Bin

AU - Yeom, Young Hoon

AU - Weitz, Eric

AU - Sachtler, Wolfgang M.H.

PY - 2004

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N2 - Reduction of NOx to N2 over zeolite-based catalysts is a multi-step reaction for which transition metal (TM) ions are helpful but not indispensable. The present state of understanding the mechanism is reviewed for the catalyzed NOx reduction with ammonia or alkanes; reduction with acetaldehyde is also sketched, but will be described in detail in a separate paper. A decisive step is the interaction of two reaction intermediates containing N atoms in different oxidation states. A favorable reaction path uses an organic molecule to reduce part of the NOx to ammonia, this product then reacts with NO + NO2 to give N 2. Isotopic labeling shows that each N2 molecule has one N atom from the NH3 intermediate, the other from NOx. N2 is formed at room temperature, if an 1:1 mixture of NO and NO 2 is in contact with an Fe/MFI catalyst covered with NH3. During NOx reduction with CH4 over Pd/zeolite catalysts, H/D exchange of methane has been observed, indicating that methane is dissociatively adsorbed on Pd0 clusters that are present in the steady-state of surface oxidation and reduction steps. BaNaY catalysts, containing negligible impurities of TM elements, catalyze NOx reduction with acetaldehyde at 200°C. In the prevailing mechanism acetaldehyde is transformed via acetate ions and nitromethane to isocyanic acid, which is hydrolyzed to NH3. Again, N2 is ultimately produced from NH3 and N2O3 via ammonium nitrite.

AB - Reduction of NOx to N2 over zeolite-based catalysts is a multi-step reaction for which transition metal (TM) ions are helpful but not indispensable. The present state of understanding the mechanism is reviewed for the catalyzed NOx reduction with ammonia or alkanes; reduction with acetaldehyde is also sketched, but will be described in detail in a separate paper. A decisive step is the interaction of two reaction intermediates containing N atoms in different oxidation states. A favorable reaction path uses an organic molecule to reduce part of the NOx to ammonia, this product then reacts with NO + NO2 to give N 2. Isotopic labeling shows that each N2 molecule has one N atom from the NH3 intermediate, the other from NOx. N2 is formed at room temperature, if an 1:1 mixture of NO and NO 2 is in contact with an Fe/MFI catalyst covered with NH3. During NOx reduction with CH4 over Pd/zeolite catalysts, H/D exchange of methane has been observed, indicating that methane is dissociatively adsorbed on Pd0 clusters that are present in the steady-state of surface oxidation and reduction steps. BaNaY catalysts, containing negligible impurities of TM elements, catalyze NOx reduction with acetaldehyde at 200°C. In the prevailing mechanism acetaldehyde is transformed via acetate ions and nitromethane to isocyanic acid, which is hydrolyzed to NH3. Again, N2 is ultimately produced from NH3 and N2O3 via ammonium nitrite.

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Reduction over zeolite-based catalysts of nitrogen oxides in emissions containing excess oxygen: Unraveling the reaction mechanism

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