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The influence of extra-framework alkali-metal cations on the adsorption of CO on CHA zeolite framework

Authors: Halamek Jakub | Bulánek Roman | Rubeš Miroslav | Bludský Ota

Year: 2024

Type of publication: ostatní - přednáška nebo poster

Page from-to: nestránkováno

Titles:

Language	Name	Abstract	Keywords
eng	The influence of extra-framework alkali-metal cations on the adsorption of CO on CHA zeolite framework	In this study, the adsorption of CO was investigated on a series of alkali-exchanged chabazite (M-CHA-x) zeolites (Si/Al = x = 2 - ∞) for the purpose of studying the structural features of the materials as well as the underlying adsorption mechanisms. The experimental approach consisted of performing transmission FTIR measurements of the CO species adsorbed on the zeolite surface at 77 K along with a subsequent recording of time-resolved spectra upon desorption. The experiments were combined with periodic DFT calculations performed by collaborators. On the basis of agreement between experimental and computational results, it was discovered that in the case of high-silica CHA materials (Si/Al > 8), single and dual adsorption site models accurately describe the system. This approach was found to be inadequate for the CHA-2 materials (esp. K-CHA-2), requiring a statistical approach due to a very large number of possible Al-configurations. The results revealed that while the 8-membered ring occupancies for both Na-CHA-2 and K-CHA-2 were very similar (0.80 vs. 0.85), this slight difference resulted in significantly different diffusivities of CO into the zeolite cages (50 vs. 90 % blocked respectively). This was corroborated by the experimental measurements. In addition, ab initio molecular dynamics simulations (AIMD) revealed that a CO molecule located in a closed K-CHA-2 cage is delocalized – corresponding to a single observed vibrational band – a finding contrasting the localized nature of the CO molecules in the high-silica CHA materials.	extra-framework; alkali-metal cations; CO adsorption; CHA zeolite