The peculiar feature of copper ion-exchanged mordenite in dinitrogen (N2) adsorption has been investigated through the measurements of infrared (IR) and emission spectra (ES) and X-ray absorption fine structure (XAFS). IR spectra provided the definitive evidence for the existence of at least two kinds of adsorption sites on the 873 K-treated copper ion-exchanged mordenite; the absorption bands centered at 2160 and 2150 cm-1 appeared when CO molecules were adsorbed. The adsorbed species assigned to the former band was desorbed at 573 K in vacuo and that to the latter one at 473 K. It was found that the site responsible for the latter band acts as effective sites for N2 adsorption. XAFS spectra also showed new bands due to the CO adsorption on copper ion at 1.48 Å, 2.52 Å, and 8.981 keV, together with bands at 1.85 Å and 8.993 keV. The former set of bands was concomitant with the appearance of an IR band at 2150 cm-1 due to the adsorbed CO species. The two bands (at 8.981 and 8.993 keV) observed in the XAFS spectra for the CO-adsorbed sample are explained in terms of the formation of a planar three- or four-coordinate site through the reaction of copper ions with CO molecules. CO adsorption also caused a significant shift of the emission band from 470 to 430 nm. This band reverted to the original position by evacuating the sample at 473 K, accompanying a liberation of CO. This makes possible the interpretation that the adsorption site responsible for respective bands at 2150 cm-1 in IR, at 430 nm in ES, and at 8.981 keV in XAFS spectra through the interaction with CO molecules is effective for N2 adsorption at ambient temperature.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry