A stable and bifunctional molybdenum based amino-MIL-101(Al) catalyst for producing mannose crystal from glucose in water

We reported a bifunctional site-isolated Lewis acid-Brønsted base metal-organic frameworks (NH₂-Mo-MIL-101(Al)) for selective epimerization and isomerization of glucose to mannose and fructose. The yields of mannose and fructose were 34.09 % and 19.25 %, respectively, at 120 °C for 40 min. The sum selectivity of mannose and fructose was 95.64 %. System characterization showed that the excellent catalytic performance may attribute to the synergistic effect of Lewis acid (MoO₂ and MoO₃) sites and Brønsted base (-NH₂) sites on NH₂-Mo-MIL-101(Al). The composition of the catalyst before and after catalysis experiment was characterized by ICP-MS. Results showed that no Mo specie was leached from NH₂-Mo-MIL-101(Al) after 5 times re-used. 97 % of catalytic efficiency was retained after 5 times reusing compared to origin NH₂-Mo-MIL-101(Al). The N-Mo chemical bonding between Mo active sites with NH₂-MIL-101(Al) skeleton enhanced the hydro-stability and hydrothermal cyclic stability. Notably, 94.13 % of total sugar recovery was achieved from reaction solution by sample crystallization process without requiring chromatographic separation. High purity of glucose (91.27 %) and mannose (88.53 %) were recovered from reaction solution. This study provided a green and feasible catalytic and recovery process for industrial production of high-yield mannose and fructose from glucose.