doi:10.1016/j.jcat.2006.10.017
Copyright © 2006 Elsevier Inc. All rights reserved.
Direct NO and N2O decomposition and NO-assisted N2O decomposition over Cu-zeolites: Elucidating the influence of the Cu
Cu distance on oxygen migration
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Pieter J. Smeetsa, Marijke H. Groothaerta, 1, Robert M. van Teeffelenb, Hugo Leemana, Emiel J.M. Hensenb and Robert A. Schoonheydta, 
, 
aCenter for Surface Chemistry and Catalysis, K.U. Leuven, Kasteelpark Arenberg 23, B-3001 Leuven, Belgium
bSchuit Institute of Catalysis, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
Received 28 June 2006;
revised 13 October 2006;
accepted 17 October 2006.
Available online 28 November 2006.
Abstract
Several zeolites of varying topology and with different Cu/Al ratios were investigated in the catalytic decomposition of NO, N2O and the NO-assisted N2O decomposition. The highest activity in the direct NO and N2O decomposition was found for bis(μ-oxo)dicopper cores in Cu-ZSM-5 followed by the EPR silent Cu in MOR, FER and BEA, while almost no activity was observed over the isolated, EPR detectable Cu sites. This sequence of decreasing activity follows the increasing average distance between Cu sites. An average volume of 35 Å3 per Cu atom (average CuCu distance 4.1 Å) appears to be a threshold value separating high and low activity. The high activity for catalysts with small CuCu distances is explained by facile oxygen migration over the Cu sites, enabling recombination into gaseous O2. When the distance between the Cu centers is increased, oxygen migration is hampered. Adding NO results in the scavenging of the deposited O atoms, thereby transporting them into the gas phase. Hence an alternative oxygen migration pathway is created that has the greatest impact on activity of the isolated EPR-detectable Cu sites and a negative effect on the bis(μ-oxo)dicopper cores in Cu-ZSM-5.
Keywords: N2O decomposition; NO decomposition; NO-assisted; N2O decomposition; Copper zeolites; Bis(μ-oxo)dicopper core; EPR silent copper
Fig. 1. Conversion of 1% N2O in He at 450 °C and at 400 °C over Cu-ZSM-5 catalysts as a function of the Cu/Al ratio.
Fig. 2. Conversion of 1% N2O at 450 °C with increasing amount of NO added for (A) the Cu-zeolites with Cu/Al 
0.22 and (B) Cu/Al > 0.35.
Fig. 3. N2 and O2 concentration profiles during 1% NO decomposition at 500 °C as a function of time.
Fig. 4. Amount of spins/g sample detected with EPR compared with the amount of Cu obtained with ICP as a function of the Cu wt%.
Fig. 5. Average volume available per Cu atom as a function of the absolute amount of EPR silent Cu atoms present.
Fig. 6. FTIR spectra of (A) Na-ZSM-5 during 0.5% N2O + 0.1% NO treatment at 450 °C and (B) CM-8.8-0.50 after switching from a 0.5% N2O/He to a 0.1% NO/He flow at 300 °C and during 0.1% NO + 0.5% N2O treatment at 300 and 450 °C.
Fig. 7. UV–vis spectra of CZ-12-0.56 during 0.5% N2O decomposition and 0.1 and 0.02% NO-assisted N2O decomposition at 400 °C.
Fig. 8. TOF of N2O decomposition (1% N2O in He) at 450 °C as a function of the amount of EPR silent Cu in the different Cu-zeolites.
Fig. 9. Conversion of 1% N2O at 450 °C as a function of volume/Cu atom in the MOR, FER and 
samples.
Scheme 1. Reaction pathways for the NO-assisted N2O decomposition.
Table 1.
Chemical and structural details of the catalysts
Table 2.
Overview of experimental conditions
Table 3.
Conversion data of direct and NO-assisted N2O decomposition
Table 4.
Spectroscopic results for the Cu-zeolites
Corresponding author. Fax: +32 16 321998.
1 Current address: DSM, P.O. Box 18, 6160 MD Geleen, The Netherlands.
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