The adsorption of carbon dioxide onto M-ZSM-5 zeolites (M = Li, Na, K, Cs) was studied by means of FTIR spectroscopy and adsorption microcalorimetry. Quantum chemical calculations, at the B3-LYP level, on the interaction of CO2 with the bare alkali-metal cations were performed to assist interpretation of the experimental results. With the likely exception of Li+, CO2 was found to undergo a two-step interaction with the metal ions. At a low equilibrium pressure linear 1:1 adducts of the type M+···OCO (M = Na+, K+, Cs+) are formed; upon increasing the CO2 equilibrium pressure, the metal cation coordinates a second CO2 molecule, forming a 2:1 adduct. Calculated (ab initio) bond lengths for the 1:1 adduct are given, as well as corresponding values of the binding energy and enthalpic term. Experimentally derived values of the main thermodynamic functions (ΔH°, ΔG°, and ΔS°) are discussed and correlated with detailed results from IR spectroscopy. The interaction cation/CO2 alone cannot account for the body of evidence, and the contribution of nearby O2- anions has to be invoked.
Experimental and quantum chemical studies on the adsorption of carbon dioxide on alkali-metal-exchanged ZSM-5 zeolites / Bonelli, Barbara; Civalleri, B.; Fubini, B.; Ugliengo, P.; Otero Areán, C.; Garrone, Edoardo. - In: JOURNAL OF PHYSICAL CHEMISTRY. B, CONDENSED MATTER, MATERIALS, SURFACES, INTERFACES & BIOPHYSICAL. - ISSN 1520-6106. - 104:47(2000), pp. 10978-10988. [10.1021/jp00055g]
|Titolo:||Experimental and quantum chemical studies on the adsorption of carbon dioxide on alkali-metal-exchanged ZSM-5 zeolites|
|Data di pubblicazione:||2000|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1021/jp00055g|
|Appare nelle tipologie:||1.1 Articolo in rivista|