The use of metal–organic frameworks (MOFs) for the encapsulation of different active entities is thoroughly reviewed. Either by following ship in a bottle or bottle around a ship approaches, active species can be encapsulated in the porous framework of different MOFs. Encapsulated species vary from polymers to organometallics and from polyoxometalates to metal nanoparticles and metal oxides. The main advantages and limitations of the use of MOFs together with the synthetic approaches followed are evaluated.

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.