Why copper ion-exchanged ZSM-5-type zeolite is so active for CO adsorption? - Comparison with adsorption properties of silver ion-exchanged ZSM-5 -

Yasushige Kuroda, Ryotaro Kumashiro, Hideo Onishi, Toshinori Mori, Hisayoshi Kobayashi, Yuzo Yoshikawa, Mahiko Nagao

Research output: Contribution to journalArticle

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Abstract

We have examined the properties of copper or silver ion-exchanged zeolites to picture the bonding nature, as well as to clarify the specificity of the electronic state of the copper ion exchanged in ZSM-type zeolite. There are a few kinds of the adsorption sites giving the IR band at around 2155 or 2190 cm-1 for CO molecule adsorbed on copper or silver ion exchanged in ZSM-5, respectively. It is clearly indicated that the property of metal-ion-exchanged ZSM-5 samples for CO adsorption is well correlated with the fact whether the parent Brönsted acid site exists or not, by comparing with the adsorption property of CO on metal-ion-supported silica-alumina or SiO2 sample. By applying the relationship between the differential adsorption heats of CO, qdiff, and the stretching vibration of adsorbed CO, vCO, the interaction between CO molecule and the copper ion exchanged in the ZSM-5 sample is well explained in terms of a σ-bonding nature, as is different from the case of Ag+-CO ZSM-5 system where the electrostatic attraction is operative. As for Ag+, the energy separation between 5s and 4d levels is expected to be large, as suggested from the data that the larger absorption energy between the electronic configuration 4d10 and the first excitation 4d95s1 as well as the larger second ionization energy of silver metal, in comparison with these values for copper ion (between 4s and 3d). As a result, we come to the conclusionthat the mixing of orbital of 4s and 3d levels plays an important role in the adsorption property of copper-ion exchanged on the Brönsted acid site.

Original languageEnglish
Pages (from-to)689-694
Number of pages6
JournalStudies in Surface Science and Catalysis
Volume132
Publication statusPublished - Jan 1 2001

ASJC Scopus subject areas

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

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