Prominent redox feature of copper ion exchanged in ZSM-5-type zeolite

Yasushige Kuroda, Ryotaro Kumashiro, Mahiko Nagao

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

The redox features of copper ion exchanged in ZSM-5 were investigated in both evacuation-oxidation-re-evacuation and evacuation-hydration-re-evacuation processes. The XANES and ESR spectra clearly indicated the conversion of Cu(II) ion exchanged in ZSM-5 into Cu(I) with increasing evacuation temperatures. The ability of Cu(I) formed to undergo a complete oxidation with O2 at 673K was certified and succeeding reduction process by heat treatment in vacuo was examined. Adsorbed amounts of CO and N2 at 298K are scarcely changed for the samples evacuated at 873K before and after O2 treatment. The extended X-ray absorption fine structure (EXAFS) spectrum exhibited a band centered at around 2.2Å through the exposure of the CuZSM-5 sample evacuated at 873K to water vapor. This band was assigned to the backscattering from the first nearest copper metal, indicating the formation of small metal particles. The production of the divalent copper ion was also evidenced by the ESR data. These results suggest that the Cu(I) species formed in the evacuation process are transformed into the Cu(II) species and metal particles; the disproportionation reaction occurs, 2Cu(I) → Cu(II) + Cu(0). As the results, it is concluded that the redox process between Cu(II) and Cu(I) is completely reproducible in the evacuation-oxidation-re-evacuation process and this is the key process in the catalytic decomposition of nitric oxides on CuZSM-5: the high stability of Cu(I) in ZSM-5. In addition, one of the causes of the poisoning by water adsorption in catalytic decomposition of NOx may be due to the release of Cu(I) in ZSM-5 through the disproportionation reaction.

Original languageEnglish
Pages (from-to)408-422
Number of pages15
JournalApplied Surface Science
Volume196
Issue number1-4
DOIs
Publication statusPublished - Aug 15 2002

Fingerprint

Copper
Metals
metal particles
Ions
copper
Oxidation
oxidation
Paramagnetic resonance
Decomposition
decomposition
ions
poisoning
Nitric oxide
Steam
X ray absorption
Backscattering
Carbon Monoxide
nitric oxide
Hydration
Water vapor

Keywords

  • Copper ion-exchanged ZSM-5-type zeolite
  • Disproportionation reaction
  • NO decomposition activity
  • Redox reaction cycle of copper ion

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Condensed Matter Physics

Cite this

Prominent redox feature of copper ion exchanged in ZSM-5-type zeolite. / Kuroda, Yasushige; Kumashiro, Ryotaro; Nagao, Mahiko.

In: Applied Surface Science, Vol. 196, No. 1-4, 15.08.2002, p. 408-422.

Research output: Contribution to journalArticle

Kuroda, Yasushige ; Kumashiro, Ryotaro ; Nagao, Mahiko. / Prominent redox feature of copper ion exchanged in ZSM-5-type zeolite. In: Applied Surface Science. 2002 ; Vol. 196, No. 1-4. pp. 408-422.
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abstract = "The redox features of copper ion exchanged in ZSM-5 were investigated in both evacuation-oxidation-re-evacuation and evacuation-hydration-re-evacuation processes. The XANES and ESR spectra clearly indicated the conversion of Cu(II) ion exchanged in ZSM-5 into Cu(I) with increasing evacuation temperatures. The ability of Cu(I) formed to undergo a complete oxidation with O2 at 673K was certified and succeeding reduction process by heat treatment in vacuo was examined. Adsorbed amounts of CO and N2 at 298K are scarcely changed for the samples evacuated at 873K before and after O2 treatment. The extended X-ray absorption fine structure (EXAFS) spectrum exhibited a band centered at around 2.2{\AA} through the exposure of the CuZSM-5 sample evacuated at 873K to water vapor. This band was assigned to the backscattering from the first nearest copper metal, indicating the formation of small metal particles. The production of the divalent copper ion was also evidenced by the ESR data. These results suggest that the Cu(I) species formed in the evacuation process are transformed into the Cu(II) species and metal particles; the disproportionation reaction occurs, 2Cu(I) → Cu(II) + Cu(0). As the results, it is concluded that the redox process between Cu(II) and Cu(I) is completely reproducible in the evacuation-oxidation-re-evacuation process and this is the key process in the catalytic decomposition of nitric oxides on CuZSM-5: the high stability of Cu(I) in ZSM-5. In addition, one of the causes of the poisoning by water adsorption in catalytic decomposition of NOx may be due to the release of Cu(I) in ZSM-5 through the disproportionation reaction.",
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N2 - The redox features of copper ion exchanged in ZSM-5 were investigated in both evacuation-oxidation-re-evacuation and evacuation-hydration-re-evacuation processes. The XANES and ESR spectra clearly indicated the conversion of Cu(II) ion exchanged in ZSM-5 into Cu(I) with increasing evacuation temperatures. The ability of Cu(I) formed to undergo a complete oxidation with O2 at 673K was certified and succeeding reduction process by heat treatment in vacuo was examined. Adsorbed amounts of CO and N2 at 298K are scarcely changed for the samples evacuated at 873K before and after O2 treatment. The extended X-ray absorption fine structure (EXAFS) spectrum exhibited a band centered at around 2.2Å through the exposure of the CuZSM-5 sample evacuated at 873K to water vapor. This band was assigned to the backscattering from the first nearest copper metal, indicating the formation of small metal particles. The production of the divalent copper ion was also evidenced by the ESR data. These results suggest that the Cu(I) species formed in the evacuation process are transformed into the Cu(II) species and metal particles; the disproportionation reaction occurs, 2Cu(I) → Cu(II) + Cu(0). As the results, it is concluded that the redox process between Cu(II) and Cu(I) is completely reproducible in the evacuation-oxidation-re-evacuation process and this is the key process in the catalytic decomposition of nitric oxides on CuZSM-5: the high stability of Cu(I) in ZSM-5. In addition, one of the causes of the poisoning by water adsorption in catalytic decomposition of NOx may be due to the release of Cu(I) in ZSM-5 through the disproportionation reaction.

AB - The redox features of copper ion exchanged in ZSM-5 were investigated in both evacuation-oxidation-re-evacuation and evacuation-hydration-re-evacuation processes. The XANES and ESR spectra clearly indicated the conversion of Cu(II) ion exchanged in ZSM-5 into Cu(I) with increasing evacuation temperatures. The ability of Cu(I) formed to undergo a complete oxidation with O2 at 673K was certified and succeeding reduction process by heat treatment in vacuo was examined. Adsorbed amounts of CO and N2 at 298K are scarcely changed for the samples evacuated at 873K before and after O2 treatment. The extended X-ray absorption fine structure (EXAFS) spectrum exhibited a band centered at around 2.2Å through the exposure of the CuZSM-5 sample evacuated at 873K to water vapor. This band was assigned to the backscattering from the first nearest copper metal, indicating the formation of small metal particles. The production of the divalent copper ion was also evidenced by the ESR data. These results suggest that the Cu(I) species formed in the evacuation process are transformed into the Cu(II) species and metal particles; the disproportionation reaction occurs, 2Cu(I) → Cu(II) + Cu(0). As the results, it is concluded that the redox process between Cu(II) and Cu(I) is completely reproducible in the evacuation-oxidation-re-evacuation process and this is the key process in the catalytic decomposition of nitric oxides on CuZSM-5: the high stability of Cu(I) in ZSM-5. In addition, one of the causes of the poisoning by water adsorption in catalytic decomposition of NOx may be due to the release of Cu(I) in ZSM-5 through the disproportionation reaction.

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