Abstract
In this work, the inclusion of free sulfonic acid groups in highly stable MOFs is explored. The synthesized catalysts have been applied in a model esterification reaction. Two metal organic frameworks bearing sulfonic acid moieties are investigated: HSO3-MIL-101(Cr) synthesized following different approaches and a new structure based on HSO3-bdc and Zr. The acidic properties, catalytic performance, deactivation and stability of the different structures are critically evaluated. In the case of MIL-101(Cr), deactivation of the sulfonic groups via formation of butanol sulfonic esters has been observed. Due to the strong interaction between –SO3 _ and the Cr open metal site where usually fluorine (F_) is located in the structure, the HSO3-MIL-101(Cr) catalysts are not stable under acidic regeneration conditions. When using Zr as a metal node, a new and stable sulfonic acid containing porous structure was synthesized. This structure showed high activity and full re-usability in the esterification of n-butanol with acetic acid. In this case, deactivation of the catalyst due to sulfonic ester formation could be reversed by reactivation under acidic conditions.
Highlights
View Article OnlineTwo metal organic frameworks bearing sulfonic acid moieties are investigated: HSO3-MIL-101(Cr) synthesized following different approaches and a new structure based on HSO3-bdc and Zr. The acidic properties, catalytic performance, deactivation and stability of the different structures are critically evaluated
During the last few decades, much effort has been put into the development of acidic solid materials such as ion-exchange resins based on sulfonic acid groups,[1] sulfated oxides based on zirconia, silica, or alumina[2] and activated carbons with different surface functional groups.[3,4,5]
HSO3-MIL-101(Cr)HCl has been synthesized according to the procedure reported by Kitagawa and co-workers, a mixture of monosodium 2-sulfoterephthalic acid (2 g, 7.5 mmol), CrO3 (0.75 g, 7.5 mmol), concentrated aqueous hydrochloric acid (12 N, 0.546 g) was dissolved in water (30 g), and it was hydrothermally treated at 453 K for 168 h
Summary
Two metal organic frameworks bearing sulfonic acid moieties are investigated: HSO3-MIL-101(Cr) synthesized following different approaches and a new structure based on HSO3-bdc and Zr. The acidic properties, catalytic performance, deactivation and stability of the different structures are critically evaluated. When using Zr as a metal node, a new and stable sulfonic acid containing porous structure was synthesized. This structure showed high activity and full re-usability in the esterification of n-butanol with acetic acid. In this case, deactivation of the catalyst due to sulfonic ester formation could be reversed by reactivation under acidic conditions
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