Low activation energy pathway for the catalyzed reduction of nitrogen oxides to N2 by ammonia

• Published in: Catalysis letters 2004-10, Vol.98 (1), p.5-9
• Main Authors: MEIJUN LI, JUAN HENAO, YEOM, Younghoon, WEITZ, Eric, SACHTLER, Wolfgang M. H
• Format: Article
• Language: English
• Subjects: Activation energy; Ammonia; Ammonium nitrate; Catalysis; Chemical reduction; Chemistry; Decomposition; Exact sciences and technology; General and physical chemistry; Ion-exchange; Nitrogen dioxide; Nitrogen oxides; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Zeolites: preparations and properties
• ISSN: 1011-372X; 1572-879X
• DOI: 10.1007/s10562-004-6441-y

A low activation energy pathway for the catalytic reduction of nitrogen oxides to N2, with reductants other than ammonia, consists of two sets of reaction steps. In the first set, part of the NOx is reduced to NH3; in the second set ammonium nitrite, NH4NO2 is formed from this NH3 and NO + NO2. The NH4NO2 thus formed decomposes at ~100 °C to N2 + H2O, even on an inert support, whereas ammonium nitrate, NH4NO3, which is also formed from NH3 and NO2 + O2, (or HNO3), decomposes only at 312 °C yielding mainly N2O. Upon applying Redhead's equations for a first order desorption to the decomposition of ammonium nitrite, an activation energiy of 22.4 is calculated which is consistent with literature data. For the reaction path via ammonium nitrite a consumption ratio of 1/1 for NO and NO2 is predicted and confirmed experimentally by injecting NO into a mixture of NH3 + NO2 flowing over a BaNa/Y catalyst. This leads to a yield increase of one N2 molecule per added molecule of NO. Little N2 is produced from NH3 + NO in the absence of NO2.