The Low Temperature Interaction of NO + O2 with a Commercial Cu-CHA Catalyst: A Chemical Trapping Study

• Published in: Topics in catalysis 2016-05, Vol.59 (8-9), p.678-685
• Main Authors: Selleri, Tommaso, Ruggeri, Maria Pia, Nova, Isabella, Tronconi, Enrico
• Format: Article
• Language: English
• Subjects: Catalysis; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Industrial Chemistry/Chemical Engineering; Pharmacy; Physical Chemistry
• ISSN: 1022-5528; 1572-9028
• DOI: 10.1007/s11244-016-0543-9

We investigate the interaction of NO + O 2 with a Cu-CHA SCR catalyst in the low temperature region. To this purpose, a well validated experimental protocol, including a combination of transient response methods, ex situ FTIR spectroscopy and chemical trapping techniques, is applied. In particular, the combination of a Cu-CHA catalyst powder and a BaO/Al 2 O 3 NOx trap in a physical mixture is used in an attempt to capture and stabilize reactive and possibly elusive NOx intermediates, which might go otherwise undetected. As a result, direct evidence for the formation of nitrites in the oxidative activation of NO over Cu-CHA is obtained. Identification of trapped nitrites intermediates has been confirmed in several ways, including: (i) their thermal decomposition to an equimolar mix of NO and NO 2 during temperature programmed desorption, (ii) N 2 formation during their reaction with NH 3 at low temperature, (iii) ex situ IR analysis of the BaO/Al 2 O 3 phase after discharge and separation from the mechanical mixture. On such a basis, a low temperature redox mechanism for NO oxidation and Standard SCR reaction over Cu-zeolite catalysts is proposed and discussed.