Open AccessStructure and Reactivity of Oxygen-Bridged Diamino Dicopper(II) Complexes in Cu-Ion-Exchanged Chabazite Catalyst for NH3-Mediated Selective Catalytic Reduction
Author(s) -
Chiara Negri,
Tommaso Selleri,
Elisa Borfecchia,
Andrea Martini,
Kirill A. Lomachenko,
Ton V. W. Janssens,
Michele Cutini,
Silvia Bordiga,
Gloria Berlier
Publication year - 2020
Publication title -
journal of the american chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.115
H-Index - 612
eISSN - 1520-5126
pISSN - 0002-7863
DOI - 10.1021/jacs.0c06270
Subject(s) - chemistry , chabazite , extended x ray absorption fine structure , catalysis , selective catalytic reduction , reactivity (psychology) , xanes , nox , inorganic chemistry , redox , diamine , oxygen , absorption (acoustics) , absorption spectroscopy , zeolite , spectroscopy , polymer chemistry , organic chemistry , medicine , alternative medicine , pathology , physics , quantum mechanics , acoustics , combustion
The NH 3 -mediated selective catalytic reduction (NH 3 -SCR) of NOx over Cu-ion-exchanged chabazite (Cu-CHA) catalysts is the basis of the technology for abatement of NOx from diesel vehicles. A crucial step in this reaction is the activation of oxygen. Under conditions for low-temperature NH 3 -SCR, oxygen only reacts with Cu I ions, which are present as mobile Cu I diamine complexes [Cu I (NH 3 ) 2 ] + . To determine the structure and reactivity of the species formed by oxidation of these Cu I diamine complexes with oxygen at 200 °C, we have followed this reaction, using a Cu-CHA catalyst with a Si/Al ratio of 15 and 2.6 wt% Cu, by X-ray absorption spectroscopies (XANES and EXAFS) and diffuse reflectance UV-Vis spectroscopy, with the support of DFT calculations and advanced EXAFS wavelet transform analysis. The results provide unprecedented direct evidence for the formation of a [Cu 2 (NH 3 ) 4 O 2 ] 2+ mobile complex with a side-on μ-η 2 ,η 2 -peroxo diamino dicopper(II) structure, accounting for 80-90% of the total Cu content. These [Cu 2 (NH 3 ) 4 O 2 ] 2+ are completely reduced to [Cu I (NH 3 ) 2 ] + at 200 °C in a mixture of NO and NH 3 . Some N 2 is formed as well, which suggests the role of the dimeric complexes in the low-temperature NH 3 -SCR reaction. The reaction of [Cu 2 (NH 3 ) 4 O 2 ] 2+ complexes with NH 3 leads to a partial reduction of the Cu without any formation of N 2 . The reaction with NO results in an almost complete reduction to Cu I , under the formation of N 2 . This indicates that the low-temperature NH 3 -SCR reaction proceeds via a reaction of these complexes with NO.