In:
Adsorption, Springer Science and Business Media LLC, Vol. 27, No. 1 ( 2021-01), p. 49-68
Abstract:
The interaction and nature of surface sites for water and methanol sorption on MFI-type zeolites and mesoporous SBA-15 were investigated by solid-state NMR spectroscopy and correlated with the desorption enthalpies determined via TGA/DSC. For siliceous Silicalite-1, 29 Si CPMAS NMR studies support stronger methanol than water interactions with SiOH groups of Q 3 -type. On siliceous SBA-15, SiOH groups of Q 2 -type are accompanied by an enhanced hydrophilicity. In aluminum-containing Na-ZSM-5, Na + cations are strong adsorption sites for water and methanol as evidenced by 23 Na MAS NMR in agreement with high desorption enthalpies of Δ H = 66–74 kJ/mol. Solid-state NMR of aluminum-containing Na-[Al]SBA-15, in contrast, has shown negligible water and methanol interactions with sodium and aluminum. Desorption enthalpies of Δ H = 44–60 kJ/mol hint at adsorption sites consisting of SiOH groups influenced by distant framework aluminum. On H-ZSM-5, Brønsted acidic OH groups are strong adsorption sites as indicated by partial protonation of water and methanol causing low-field shifts of their 1 H MAS NMR signals and enhanced desorption enthalpies. Due to the small number of Brønsted acid sites in aluminum-containing H-[Al]SBA-15, water and methanol adsorption on this material is suggested to mainly occur at SiOH groups with distant framework aluminum species, as in the case of Na-[Al] SBA-15.
Type of Medium:
Online Resource
ISSN:
0929-5607
,
1572-8757
DOI:
10.1007/s10450-020-00275-8
Language:
English
Publisher:
Springer Science and Business Media LLC
Publication Date:
2021
detail.hit.zdb_id:
1483298-7
