Transfer hydrogenation of 5-Hydroxymethylfurfural to 2,5-dihydroxymethylfuran by synergistic catalysis with a mixture of ZIF-8 and UiO-66-NH2

The metal-organic framework materials ZIF-8 and UiO-66-NH 2 , synthesized by hydrothermal methods, were characterized in detail and combined to catalyze the transfer hydrogenation of 5-hydroxymethylfurfural (5-HMF) to 2,5-di(hydroxymethyl)furan (2,5-DHMF) using isopropanol as the hydrogen source. The ZIF-8/UiO-66-NH 2 catalyst mixture exhibited abundant Lewis acid-base sites and a hierarchical multiporous structure with a large specific surface area (564.0 m 2 /g). The conversion of 5-HMF reached 98.2 %, and the selectivity and yield of 2,5-DHMF were 96.2 % and 94.5 %, respectively. The recycling performance of ZIF-8/UiO-66-NH 2 was also investigated, and the conversion of 5-HMF and selectivity of 2,5-DHMF significantly decreased to 78.4 % and 79.1 % in the second run, respectively. The loss of −NH 2 groups was found to be the main reason for the decrease in activity. However, the catalytic activity of the recovered catalyst can be almost completely restored by the addition of a small amount of fresh UiO-66-NH 2 and ZIF-8, and the conversion of 5-HMF and selectivity of 2,5-DHMF were increased to 89.4 % and 95.5 %, respectively. In the proposed reaction mechanism, Lewis acid-base sites play important roles and exhibit a synergistic catalytic effect in the selective conversion of 5-HMF to 2,5-DHMF.