Oxidation state of copper ions in ZSM-5 zeolite

Abstract

Cu(II)-ZSM-5 samples were prepared with different copper loadings from under- to over-exchanged levels. The adsorption of carbon monoxide and nitrous oxide took place at room temperature and was studied by microcalorimetric methods. The adsorbed amounts of both gases and differential heats of adsorption depended on the copper content in the zeolitic structure. The coordination and oxidation states of copper ions in the investigated samples were studied by means of diffuse reflectance UV-VIS-NIR and FTIR spectroscopy. After pretreatment in vacuum, the coordination of copper ions was changed. As a result of this pretreatment, Cu(II) ions were reduced to Cu(I). N2O and CO molecules were adsorbed at these reduced copper species.