Temperature-programmed reduction with NO as a characterization of active Cu in Cu-CHA catalysts for NH3-SCR. Issue 10 (30th April 2019)

• Record Type: Journal Article
• Authors: Hammershøi, Peter S.; Negri, Chiara; Berlier, Gloria; Bordiga, Silvia; Beato, Pablo; Janssens, Ton V. W.
• Is Part Of: Catalysis science & technology. Volume 9:Issue 10(2019)
• Page Start: 2608
• Page End: 2619
• Publication Date: 2019-04-30
• Subjects: Catalysis -- Periodicals; 541.395
• DOI: 10.1039/c9cy00358d
• Languages: English
• ISSNs: 2044-4753

Abstract

Abstract : The NH3 -SCR activity of Cu-CHA catalysts is related to the ability to form [Cu II (NO3 )] + . Abstract : Temperature programmed reduction with NO (NO-TPR) is introduced as a characterization method, by monitoring the reduction of Cu II to Cu I in a mixture of NH3 and NO. Since the NO-TPR method is based on the oxidation and reduction half cycles of the NH3 -SCR reaction, quantitative information about the amount of active Cu in Cu-CHA is obtained. Furthermore, information on the stability and reactivity of reaction intermediates in the NH3 -SCR cycle is obtained as well. The reduction of the Cu is followed by monitoring the consumption of NO, after oxidation of the catalyst in O2 or a mixture of NO and O2 to form the Cu II state. Two distinct states of the Cu are revealed. The first state, corresponding to the reduction of a Cu-oxide species, is reduced around 130 °C and is observed at low Cu content only. The second state corresponds to the reduction of a Cu-nitrate species around 200–230 °C. The low-temperature activity of Cu-chabazite catalysts with low Cu content show the same trend as the Cu-nitrate species observed in NO-TPR. The fraction of Cu-oxide in NO-TPR decreases with increasing Cu content, leading to a non-linear dependence of the NH3 -SCR activity on the Cu-content. At high Cu content, all Cu forms a stable Cu-nitrate species, and the NH3 -SCR activity becomes proportional to the Cu content. This agrees well with the known behavior of Cu-CHA catalysts, indicating that NO-TPR seems to be a viable method for the characterization of Cu-CHA materials as NH3 -SCR catalysts.