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Title: In-situ DRIFTS measurements for the mechanistic study of NO oxidation over a commercial Cu-CHA catalyst

We report a mechanistic DRIFTS in-situ study of NO2, NO + O2 and NO adsorption on a commercial Cu-CHA catalyst for NH3-SCR of NOx. Both pre-reduced and pre-oxidized catalyst samples were investigated with the aim of clarifying mechanistic aspects of the NO oxidation to NO2 as a preliminary step towards the study of the Standard SCR reaction mechanism at low temperatures. Nitrosonium cations (NO+, N formal oxidation state = +3) were identified as key surface intermediates in the process of NO (+2) oxidation to NO2 (+4) and nitrates (+5). While NO+ and nitrates were formed simultaneously upon catalyst exposure to NO2, nitrates evolved consecutively to NO+ when the catalyst was exposed to NO + O2, suggesting that nitrite-like species, and not NO2, are formed as the primary products of the NO oxidative activation over Cu-CHA. Upon catalyst exposure to NO only, i.e. in the absence of gaseous O2, NO+ and then nitrates were formed on a pre-oxidized sample but not on a pre-reduced one, which demonstrates the red-ox nature of the NO oxidation mechanism. The negative effect of H2O on NO+ and nitrates formation was also clearly established. Assuming Cu dimers as the active sites for NO oxidation to NO2,more » we propose a mechanism which reconciles all the experimental observations. Specifically, we show that such a mechanism also explains the observed kinetic effects of H2O, O2 and NO2 on the NO oxidation activity of the investigated Cu zeolite catalyst.« less
Authors:
 [1] ;  [1] ;  [1] ;  [2] ;  [2] ;  [2]
  1. Politecnico di Milano, Milano (Italy)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
OSTI Identifier:
1207044
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Applied Catalysis. B, Environmental
Additional Journal Information:
Journal Volume: 166; Journal ID: ISSN 0926-3373
Publisher:
Elsevier
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY Cu-Chabazite catalyst; NO oxidation; NH3 SCR mechanism; nitrates; nitrosonium ion