Interaction of CO probe molecules with Cu(+) in MCM-22 zeolite

Abstract

The interaction of CO probe with copper exchanged MCM-22 zeolite is studied. Particularly, the heterogeneity of Cu(+) ions is examined. For this purpose, combined CO adsorption microcalorimetry with FTIR of CO adsorption/desorption at RT and elevated temperature is originally exploited. Contribution brings the first experimental evidence for three families of Cu(+) ions differing in the interaction energy with CO and exhibiting Qdiff around 107, 100–97 and ⩽92kJmol−1, respectively. The energy distribution determined from calorimetry and desorption curves is due to copper coordination differences. Despite wide energetic distribution of carbonyls, only two bands in IR spectra at 2159 and 2150cm−1 are observed. Similarly to other zeolites, Cu(+) loses its original coordination to framework during the CO adsorption. The preferred trigonal planar geometry with CO and two zeolite oxygen gives rise to the band at 2159cm−1. Peculiarly for MCM-22, significant amount of Cu(+) ions stay three-coordinated to the zeolite after CO adsorption, relate to mediate interaction energies and correspond to the band at 2150cm−1. Characteristic changes on the IR spectrum revealed that the enhanced movement of ions after CO exposure occurs at higher temperature. The influence of zeolite composition, namely Cu loading and Si/Al ratio, on the character of IR spectrum and population of energetic components is discussed.