Variable-temperature FT-IR studies on the thermodynamics of carbon dioxide adsorption on a faujasite-type H-Y zeolite

Adsorption of carbon dioxide on a faujasite-type H-Y zeolite (Si:Al = 2.6:1) was studied by variable-temperature (200–290 K range) infrared spectroscopy. Adsorbed CO 2 molecules interact with the Brønsted acid Si(OH)Al groups located inside the zeolite supercage, bringing about a characteristic bathochromic shift of the O–H stretching mode from 3645 cm −1 (free OH group) to 3540 cm −1 (hydrogen-bonded CO 2 adsorption complex). Simultaneously, the asymmetric ( ν 3) mode of adsorbed CO 2 is observed at 2353 cm −1. From the observed variation of the integrated intensity of the 3645 and 2353 cm −1 IR absorption bands upon changing temperature, corresponding values of standard adsorption enthalpy and entropy were found to be Δ H° = −28.5(±1) kJ mol −1 and Δ S° = −129(±10) J mol −1 K −1. Comparison with the reported values of Δ H° for CO 2 adsorption on other zeolites is briefly discussed.