Mesoporous zirconium phosphonate materials as efficient water-tolerable solid acid catalysts

Abstract

Mesoporous organic–inorganic hybrid zirconium phosphonate materials (ZrHEDP, ZrATMP and ZrEDTMPS) with organic groups bridged in the frameworks are synthesized by using 1-hydroxyethylidene-1,1′-diphosphonic acid (HEDP), amino tri(methylene phosphonic acid) (ATMP) and sodium salt of ethylene diamine tetra(methylene phosphonic acid) (EDTMPS) as coupling molecules, respectively, in the presence of the surfactant cetyltrimethylammonium bromide. The obtained hybrid mesostructures exhibited high surface areas of 310–749 m² g⁻¹, uniform pore sizes of 3.4–4.2 nm and large pore volumes of 0.42–0.74 cm³ g⁻¹, as well as H⁺ exchange capacities of 1.25–1.92 mmol g⁻¹, which are catalytically active for ethyl acetate hydrolysis in an aqueous medium and for water-produced acetic acid esterifications of ethanol or cyclohexanol. These water-tolerable solid acid catalysts possess superior stability, as revealed by recycling for four times in the cyclohexanol esterification of acetic acid with well retained textual properties and acid active sites. The good preservation of active acid sites on the pore surfaces of the prepared mesoporous zirconium phosphonate hybrid materials is related to the hydrophobic nature of organic groups integrated into the hybrid framework.