Postsynthetic acid modification of amino-tagged metal-organic frameworks: Structure-function relationship for catalytic 5-hydroxymethylfurfural synthesis

Developing an efficient and selective catalyst for the dehydration of fructose to 5-hydroxymethylfurfural(HMF) is significant for biomass conversion. Herein, a metal-organic framework(MOF) with acidity and strong hydrophobicity is first reported by the condensation of amino-tagged MOFs with mercapto carboxylic acids and subsequent oxidation. The hydrophobic acidic MOFs possess acid densities ranging from 0.2-1.0 mmol·g, HO contact angles of 114°-125°, and specific surface areas above260 m~2·g. Compared to the methyl sulfo-functionalized MOF, the benzene sulfo-functionalized MOF with a strong hydrophobicity shows much higher activity and selectivity for the conversion of fructose to 5-hydroxymethylfurfural. In particular, 2.99%(mass) UiO-PhSOH shows the best catalytic performance with a 90.4% HMF yield due to its suitable hydrophobicity and abundant acidic sites. Moreover,the catalyst shows great stability after recycling for 5 runs. This work provides an interesting design strategy for the preparation of hydrophobic acidic MOFs and shows the powerful synergistic effect of acidity and hydrophobicity.