Effect of aluminum and sodium on the sorption of water and methanol in microporous MFI-type zeolites and mesoporous SBA-15 materials

• Published in: Adsorption : journal of the International Adsorption Society Vol. 27; no. 1; pp. 49 - 68
• Main Authors: Li, Zheng, Rieg, Carolin, Beurer, Ann-Katrin, Benz, Michael, Bender, Johannes, Schneck, Christof, Traa, Yvonne, Dyballa, Michael, Hunger, Michael
• Format: Journal Article
• Language: English
• Published: New York Springer US 2021; Springer Nature B.V
• Subjects: Adsorption; Aluminum; Chemistry; Chemistry and Materials Science; Desorption; Engineering Thermodynamics; Enthalpy; Heat and Mass Transfer; Industrial Chemistry/Chemical Engineering; Methanol; NMR spectroscopy; Protonation; Silicalite; Sodium; Solid state; Sorption; Surfaces and Interfaces; Thin Films; Zeolites; Methanol adsorption; Desorption enthalpies; Water adsorption; Mesoporous SBA-15; Solid-state NMR spectroscopy; MFI-type zeolites
• ISSN: 0929-5607; 1572-8757
• DOI: 10.1007/s10450-020-00275-8

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.