Synergistic Fe(iii) and acid sites in SiW@MIL-100(Fe) catalyst prompt the synthesis of p-xylene from biomass derivatives

Abstract

The construction of aromatic skeleton structures by the Diels–Alder reaction is a synthetic route to obtain substitutes for petrochemical products using biomass as a raw material. In this work, a class of SiW@MIL-100(Fe)-n (n = 1–4) catalysts containing silicotungstic acid (SiW) encaged in MIL-100(Fe) was synthesized for the mimic synthesis of p-xylene (PX). SiW@MIL-100(Fe)-3 was applied to catalyze the reaction of 2,5-dimethylfuran and acrylic acid (AA) to give aromatic products (yield 94%, PX yield = 80.1%) at 140 °C under ambient pressure. The synergistic effect between the metal centers and Lewis/Brønsted acid was increased due to the confinement effect in the cage of MIL-100(Fe). The Fe(III) sites catalyzed the decarboxylation of AA via a free radical process, avoiding the formation of the 2,5-dimethylbenzoic acid intermediate. Two types of acid sites along with the reactants as well as the reversibly adsorbed water promoted the formation of hydrogen bonds with protons from SiW, which accelerated the dehydration reaction. This strategy provides a route for the construction of aromatic skeletons from biomass derivatives by MOF-based solid acid catalysts.