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
✍ Scribed by Seung-Kyu Park; Vadim Kurshev; Zhaohua Luan; Chul Wee Lee; Larry Kevan
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 312 KB
- Volume
- 38
- Category
- Article
- ISSN
- 1387-1811
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✦ Synopsis
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 paramagnetic Cu(II)±OH À with ®ve coordinated water molecules. Upon thermal dehydration, the ESR intensity decreases by about 85%, and it is suggested that Cu(I) and Cu(II)±O À are formed among other possible species. The remaining isolated paramagnetic Cu(II) is identi®ed by ESR as three dierent species: I, II and III with g k values of 2.314, 2.301 and 2.272, respectively. After NO adsorption onto dehydrated Cu-ZSM-5, NO interactions with Cu(I), Cu(II)±O À and Cu(II) have been studied by ESR and fourier transform infrared spectroscopy. It is suggested that Cu(II)±O À interacts with NO to form Cu(I)±(NO 2 ) 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)±NO and Cu(I)±(NO) 2 of which the latter further transforms to Cu(II)±(N 2 O)O À . Among the three paramagnetic Cu(II) ions, only species III reacts with NO to form Cu(II)±NO; the other two Cu(II) species are inactive toward NO adsorption. A schematic mechanism based on these and earlier results is proposed for NO adsorption, interaction and transformation over Cu-ZSM-5.