Re-examining the interpretation of CO adsorbed on Lewis acid sites of alkali metal-exchanged MOR zeolite

0521835 - ÚOCHB 2021 RIV NL eng J - Journal Article
Bulánek, R. - Koudelková, E. - Trachta, Michal - Bludský, Ota - Rubeš, Miroslav
Re-examining the interpretation of CO adsorbed on Lewis acid sites of alkali metal-exchanged MOR zeolite.
Microporous and Mesoporous Materials. Roč. 296, April (2020), č. článku 110007. ISSN 1387-1811. E-ISSN 1873-3093
R&D Projects: GA ČR(CZ) GA17-07642S
Institutional support: RVO:61388963
Keywords : CO * zeolites * Lewis acid sites * ab initio calculations * isosteric heats * IR spectra
OECD category: Physical chemistry
Impact factor: 5.455, year: 2020
Method of publishing: Limited access
https://www.sciencedirect.com/science/article/pii/S138718112030010X?via%3Dihub

The interaction of CO with alkali metal-exchanged mordenite has been investigated by means of IR spectroscopy and calorimetry along with theoretical calculations based on DFT corrected to coupled-cluster accuracy (DFT/CC). It has been convincingly shown that Li+ is at least partially exchanged into the constricted part of the MOR structure as manifested by the low-frequency band at 2181 cm−1 and the isosteric heat of 44 kJ/mol. In the case of Na-MOR samples, significant changes have been observed in the stabilities of high- (2177 cm−1) and low-frequency (2165 cm−1) bands upon CO desorption, with the change of the Si/Al ratio from 40 to 9. Based on the kinetic measurements, it can be concluded that a crucial role in the MOR material is played by diffusion limitations, which are significantly influenced by the Si/Al ratio and the size of the cations. Similar effects also result in the increased stability of the 2138 cm−1 band of Na/K-MOR samples with higher Al content, where the “gate” effect is observed upon N2 adsorption. The dual cationic sites are directly observed only for the K-MOR sample via the weak band around 2150 cm−1. The formation of dual cationic sites cannot be completely ruled out in the case of Na-MOR, but their presence is most likely hidden in the low-frequency band.
Permanent Link: http://hdl.handle.net/11104/0306392