Identification of nitrites/HONO as primary products of NO oxidation over Fe-ZSM-5 and their role in the Standard SCR mechanism: A chemical trapping study

• Published in: Journal of catalysis 2014-03, Vol.311, p.266-270
• Main Authors: Ruggeri, Maria Pia, Selleri, Tommaso, Colombo, Massimo, Nova, Isabella, Tronconi, Enrico
• Format: Article
• Language: English
• Subjects: Catalysis; Chemical trapping; Chemicals; Chemistry; Exact sciences and technology; Fe-zeolite SCR catalysts; General and physical chemistry; Ion-exchange; Nitric oxide; Nitrification; Nitrites; Nitrous acid; NO oxidation; Oxidation; Standard SCR mechanism; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Zeolites: preparations and properties
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2013.11.028

•Standard SCR/NO oxidation mechanisms investigated by Chemical Trapping techniques.•NO+O2 fed to a mechanical mixture of Fe-ZSM5 catalyst and BaO/Al2O3 trap.•Nitrite intermediates are formed on Fe sites and stored on BaO via gas-phase HONO.•Identification of nitrites on BaO/Al2O3 by ex situ IR analysis.•Confirmation of nitrites storage by TPD and TPSR runs with NH3. We present direct evidence for the formation of nitrites/HONO in the oxidative activation of NO over Fe-zeolites. Exposure of a Fe-ZSM-5+BaO/Al2O3 physical mixture to NO+O2 at 120°C resulted in forming nitrites on Fe-sites and trapping them on BaO via gas-phase equilibrium with HONO. Identification of nitrites was confirmed by: (i) their thermal decomposition to an equimolar mix of NO and NO2 during TPD, (ii) N2 formation during their reaction with NH3 at 120°C, (iii) ex situ IR analysis of the BaO powder after discharge and separation of the mechanical mixture. The reactivity data suggest that nitrites/HONO are intermediates both in the NO oxidation to NO2 and in the Standard SCR reactions.