Synthesis and characterization of butylamine-functionalized Cr(III)–MOF–SO3H: Synergistic effect of the hydrophobic moiety on Cr(III)–MOF–SO3H in esterification reactions

Abstract

Mesoporous solid acid catalysts with partially hydrophobic moieties, [Cr3O(BDC–SO3H)3−x(BDC–SO3NH3Bu)x]n, were prepared from [Cr3O(BDC–SO3H)3]n (MIL-101(Cr)–SO3H) and BuNH2 for the first time and then characterized by the Brunauer–Emmet–Teller (BET) technique, powder X-ray diffraction, field emission electron microscopy, Fourier transform infrared spectroscopy, and thermal and elemental analyses. The nitrogen adsorption–desorption study showed that the specific surface area and total pore volume of MIL-101(Cr)–SO3H decreased after the reaction with butylamine and formation of [Cr3O(BDC–SO3H)3−x(BDC–SO3NH3Bu)x]n. The prepared materials were used as catalysts to investigate the impact of hydrophobic moieties in esterification yields of phthalic anhydride with several alcohols as a probe reaction. The presence of butylamine as a hydrophobic group on MIL-101(Cr)–SO3H increases the esterification yield significantly for hydrophilic alcohols under solvent-free conditions. Moreover, results showed that [Cr3O(BDC–SO3H)3−x(BDC–SO3NH3Bu)x]n can be recovered and reused for several consecutive reactions without significant loss in catalyst activity.