Experimental and quantum chemical studies on the adsorption of carbon dioxide on alkali-metal-exchanged ZSM-5 zeolites

Citation
B. Bonelli et al., Experimental and quantum chemical studies on the adsorption of carbon dioxide on alkali-metal-exchanged ZSM-5 zeolites, J PHYS CH B, 104(47), 2000, pp. 10978-10988
Citations number
35
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF PHYSICAL CHEMISTRY B
ISSN journal
15206106 → ACNP
Volume
104
Issue
47
Year of publication
2000
Pages
10978 - 10988
Database
ISI
SICI code
1520-6106(20001130)104:47<10978:EAQCSO>2.0.ZU;2-W
Abstract
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 C O2 with the bare alkali-metal cations were performed to assist interpretati on of the experimental results. With the likely exception of Li+, CO2 was f ound to undergo a two-step interaction with the metal ions. At a low equili brium pressure linear 1:1 adducts of the type M+. . .O=C=O (M = Na+, K+, Cs +) are formed; upon increasing the CO2 equilibrium pressure, the metal cati on 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 va lues of the main thermodynamic functions (DeltaH(degrees), DeltaG degrees, and DeltaS degrees) are discussed and correlated with detailed results from IR spectroscopy. The interaction cation/CO2 alone cannot account for the b ody of evidence, and the contribution of nearby O2- anions has to be invoke d.