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 CO2 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 CO2 adsorption complex). Simultaneously, the asymmetric (ν3) mode of adsorbed CO2 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 ΔH° = −28.5(±1) kJ mol−1 and ΔS° = −129(±10) J mol−1 K−1. Comparison with the reported values of ΔH° for CO2 adsorption on other zeolites is briefly discussed.