doi:10.1016/j.jcat.2003.08.009
Copyright © 2003 Elsevier Inc. All rights reserved.
An operando optical fiber UV–vis spectroscopic study of the catalytic decomposition of NO and N2O over Cu-ZSM-5
References and further reading may be available for this article. To view references and further reading you must
purchase this article.
Marijke H. Groothaert, Kristof Lievens, Hugo Leeman, Bert M. Weckhuysen and Robert A. Schoonheydt
, 
Center for Surface Chemistry and Catalysis, K.U. Leuven, Kasteelpark Arenberg 23, B-3001, Leuven, Belgium
Received 16 April 2003;
revised 12 August 2003;
accepted 12 August 2003. ;
Available online 24 October 2003.
Abstract
The role of the bis(μ-oxo)dicopper core, i.e., [Cu2(μ-O)2]2+, in the decomposition of NO and N2O by the Cu-ZSM-5 zeolite has been studied with combined operando UV–vis monitoring of the catalyst and on-line GC analysis. An optical fiber was mounted on the outer surface of the quartz wall of the plug-flow reactor and collected the UV–vis diffuse reflectance spectra under true catalytic conditions. Measurement under transient reaction conditions indicated that [Cu2(μ-O)2]2+ is formed by O abstraction of N2O, which is an intermediate in the NO decomposition. This conversion of N2O to N2 and O2 is strongly retarded below 673 K. Above 673 K, the produced [Cu2(μ-O)2]2+ fulfills the role of O2 release, guaranteeing the self-reduction of the catalytic site. Studying the NO decomposition as a function of the O2 content in the feed strongly suggested that O2 release from [Cu2(μ-O)2]2+ is rate limiting in the NO decomposition at 773 K.
Author Keywords: Cu-ZSM-5; bis(μ-oxo)dicopper; NO decomposition; N2O decomposition; UV–vis spectroscopy; Operando spectroscopy
Fig. 1. Scheme of the fiber optic UV–vis spectrometer and reactor setup.
Fig. 2. Evolution of the in situ UV–vis spectra of CZ-31-0.58 during calcination. Dotted lines represent the spectra collected at 503, 603, 633, 673, 743, 773, and 773 K (15 min). Full lines represent the spectra collected after 2 h at 773 K and after cooling to room temperature in O
2 atmosphere.
Fig. 3. In situ UV–vis spectra of CZ-31-0.58 at 773 K during switch from 100 mol% O
2 to 1 mol% NO/He flow. At 0 min the flows were switched and spectra were recorded every 4 min 15 s.
Fig. 4. (a) Evolution of the reactor outlet composition of CZ-31-0.58 upon admission of 1 mol% NO in He at 773 K (900 h
−1 GHSV). (b) Corresponding evolution of the operando UV–vis spectra. “0 min” corresponds with the pretreated sample in He and spectra were recorded every 1 min and 1000 scans of 50 ms constitute one spectrum.
Fig. 5. (a) Catalytic activity of CZ-31-0.58 for the decomposition of NO (1 mol% in He; 900 h
−1 GHSV) as function of the temperature. (b) Corresponding operando UV–vis spectra at temperature intervals of 50 K.
Fig. 6. Catalytic activity as function of the Cu/Al ratio of the CZ-12 series of samples: (a) contacted with 1 mol% NO in He (900 h
−1 GHSV); (b) contacted with 2 mol% NO in He (2700 h
−1 GHSV). TOF (toward N
2 and O
2) as function of the Cu/Al ratio of the CZ-12 series of samples: (c) contacted with 1 mol% NO in He (900 h
−1 GHSV); (d) contacted with 2 mol% NO in He (2700 h
−1 GHSV).
Fig. 7. Vertical stacking of the in situ UV–vis–NIR spectra of the calcined CZ-12 series of samples with increasing Cu/Al ratio: Cu/Al=0.10, Cu/Al=0.22, Cu/Al=0.31, Cu/Al=0.38, Cu/Al=0.54, and Cu/Al=0.58.
Fig. 8. (a) Catalytic activity of CZ-31-0.58 for the decomposition of NO (1 mol%; 900 h
−1 GHSV) at 773 K as function of the O
2 concentration in the feed. After feeding 16 mol% O
2, the O
2 concentration was again set to 0 mol% and the asterisk gives the corresponding activity. (b) Corresponding operando UV–vis spectra.
Fig. 9. (a) Catalytic activity of CZ-31-0.58 for the decomposition of N
2O (1 mol%; 900 h
−1 GHSV) as function of the temperature. (b) Corresponding operando UV–vis spectra at temperature intervals of 50 K.
Fig. 10. (a) Catalytic activity of CZ-31-0.58 for the decomposition of N
2O (1 mol%; 900 h
−1 GHSV) during the temperature switch from 723 to 673 K. At 0 min the temperature decrease of 5 K min
−1 was started. (b) Corresponding operando UV–vis spectra (spectra were recorded every 3 min and 1000 scans of 50 ms constitute one spectrum).
Scheme 1. Proposed reaction mechanism for the decomposition of NO and N
2O.
Table 1. Summary of the treatments of the Cu-ZSM-5 samples

Table 2. Catalytic results of CZ-12 series of samples

Corresponding author.