Microcalorimetric and FTIR Study of the Adsorption of Carbon Dioxide on Alkali-Metal Exchanged FER Zeolites

Adsorption of CO2 on alkali-metal exchanged (Li+, Na+, K+) FER zeolites was investigated by means of microcalorimetry and FTIR spectroscopy. The adsorption enthalpies strongly depend on coverage for all investigated materials and they are also influenced by concentration of Al in the framework. Especially, samples of Na- and K-FER with lower Si/Al ratio (8.6) exhibited substantially larger initial interaction energy than samples with Si/Al 27.5. Differences in zero-coverage adsorption energy of zeolites with different cation concentration (Si/Al ratio) are 9 and 7.2 kJ/mol for Na- and K-FER zeolites respectively. This phenomenon is attributed to formation of bridged CO2 adsorption complexes formed between two cations, which are characterized by IR absorption band of nu(3) stretching vibration mode at 2370 and 2357 cm(-1) for Na- and K-FER respectively.