期刊
TOPICS IN CATALYSIS
卷 59, 期 8-9, 页码 678-685出版社
SPRINGER/PLENUM PUBLISHERS
DOI: 10.1007/s11244-016-0543-9
关键词
NO oxidation; Standard SCR mechanism; Cu-zeolite catalysts; Chemical trapping; Nitrites
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/Al2O3 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 NO2 during temperature programmed desorption, (ii) N-2 formation during their reaction with NH3 at low temperature, (iii) ex situ IR analysis of the BaO/Al2O3 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.
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