Study of adsorption sites heterogeneity in zeolites by means of coupled microcalorimetry with volumetry

• Published in: Journal of thermal analysis and calorimetry 2011-08, Vol.105 (2), p.443-449
• Main Authors: Bulánek, Roman, Frolich, Karel, Frýdová, Eva, Čičmanec, Pavel
• Format: Article
• Language: English
• Subjects: Adsorption; Aluminum; Analytical Chemistry; Carbon dioxide; Cations; Chemistry; Chemistry and Materials Science; Exact sciences and technology; General and physical chemistry; Heterogeneity; Inorganic Chemistry; Ion-exchange; Measurement Science and Instrumentation; MFI; Physical Chemistry; Polymer Sciences; Surface chemistry; Surface physical chemistry; Zeolites; Zeolites: preparations and properties
• ISSN: 1388-6150; 1588-2926; 1572-8943
• DOI: 10.1007/s10973-010-1108-y

Adsorption of CO 2 as probe molecule on alkali-metal zeolites of MFI structure was investigated by joint volumetry–calorimetry. Consideration was given to the interpretation of the heat evolved when a probe molecule is adsorbed on the surface. In particular, the number and the strength of adsorption sites are discussed as functions of zeolite structure, concentration, and nature of extra-framework cation. The adsorption heats ( q iso ) of CO 2 interaction with alkali-metal cations decrease for MFI zeolite with high Si/Al in the sequence Li +  > Na +  > K + from 54 kJ/mol to 49 and 43 kJ/mol, respectively. In addition, the adsorption heats are influenced by concentration of Al in the framework. This phenomenon is attributed to formation of bridged CO 2 adsorption complexes formed between two cations. On the base of quantitative analysis of adsorption processes, presence of geminal adsorption complexes was suggested for adsorption at higher equilibrium pressures.