Thermodynamics of CO probe molecule adsorption on Cu–FER-zeolite comparison of TPD, FTIR, and microcalorimetry results

Abstract

The existence of the new type of the adsorption complexes of carbon monoxide, where CO molecule interacts simultaneously with both copper and potassium cation, formed on so-called heterogeneous dual adsorption sites was detected by the FTIR spectroscopy and temperature programmed desorption technique (TPD) in the Cu, K–FER zeolite samples. The time-resolved IR spectroscopy and TPD experiments also proved their lower stability in the comparison with the classical monodentate adsorption complexes. The TPD curves of these materials exhibited low temperature desorption peak which was ascribed to these sites. The energetic parameters (i.e., energy and entropy of adsorption) as well as distribution of all present Cu+ sites were obtained by the fitting of TPD data to the phenomenological model. Obtained results suggest that the heterogeneous dual sites are special form of the adsorption sites localized on the wall of channels destabilized due to significantly higher change of the entropy of adsorption. Direct microcalorimetric measurement proved energetic equality of single and heterogeneous dual sites together with the validity of the adsorption energy values obtained from TPD.