TY - JOUR
T1 - Reduction over zeolite-based catalysts of nitrogen oxides in emissions containing excess oxygen
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.
N1 - Funding Information:
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.
PY - 2004
Y1 - 2004
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.
KW - Reduction
KW - Transition metal ions
KW - Zeolite-based catalysts
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U2 - 10.1016/j.cattod.2004.05.002
DO - 10.1016/j.cattod.2004.05.002
M3 - Article
AN - SCOPUS:4544268827
SN - 0920-5861
VL - 96
SP - 1
EP - 10
JO - Catalysis Today
JF - Catalysis Today
IS - 1-2
ER -