Reaction of NO with copper ions in Cu(II)-exchanged ZSM-5 zeolite: electron spin resonance, electron spin echo modulation and Fourier transform infrared spectroscopy
Sk. Park et al., Reaction of NO with copper ions in Cu(II)-exchanged ZSM-5 zeolite: electron spin resonance, electron spin echo modulation and Fourier transform infrared spectroscopy, MICROP M M, 38(2-3), 2000, pp. 255-266
Dehydration of Cu(II)-exchanged ZSM-5 and rehydration have been studied by
electron spin resonance (ESR) and electron spin echo modulation (ESEM). The
ESEM results indicate that Cu(II) is present in hydrated Cu-ZSM-5 as param
agnetic Cu(II)-OH- with five coordinated water molecules. Upon thermal dehy
dration, the ESR intensity decreases by about 85%, and it is suggested that
Cu(I) rind Cu(II)-O- are formed among other possible species. The remainin
g isolated paramagnetic Cu(II) is identified by ESR as three different spec
ies: I, II and III with g(parallel to) values of 2.314, 2.301 and 2.272, re
spectively. After NO adsorption onto dehydrated Cu-ZSM-5, NO interactions w
ith Cu(I), Cu(II)-O- and Cu(II) have been studied by ESR smd fourier transf
orm infrared spectroscopy. It is suggested that Cu(II)-O- interacts with NO
to form Cu(I)-(NO2) and that further interaction with NO yields Cu(II)-(NO
2)(NO). Cu(I) is also suggested to react with one or two NO to form Cu(I)-N
O and Cu(I)-(NO)(2) of which the latter further transforms to Cu(II)-(N2O)O
-. Among the three paramagnetic Cu(II) ions, only species III reacts with N
O to form Cu(II)-NO; the other two Cu(II) species are inactive toward NO ad
sorption. A schematic mechanism based on these and earlier results is propo
sed for NO adsorption, interaction and transformation over Cu-ZSM-5. (C) 20
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