XANES, EXAFS and FTIR characterization of copper-exchanged mordenite

Abstract

Over-exchanged Cu^I-mordenite has been prepared by gas phase reaction between the protonic form of the zeolite and Cu^ICl. No evidence was found for the presence of Cu^II ions or copper species in microaggregates. EXAFS analysis revealed that Cu^I ions in the outgassed zeolite are surrounded by 2.5 ± 0.35 oxygen atoms of the zeolite framework, the average Cu^I–O distance being 1.96 (±0.02) Å. Both X-ray absorption and FTIR spectroscopy showed that the zeolite adsorbs CO at room temperature with formation of Cu^I(CO)_n adducts (n = 1, 2). At liquid nitrogen temperature, tricarbonyl species were also formed. The IR spectra of adsorbed CO showed broad and complex bands, which is consistent with the fact that the zeolite contains different types of cation sites accessible to carbon monoxide. This was further demonstrated by comparison with corresponding IR and EXAFS spectra of CO adsorbed on Cu^I-ZSM-5.