One-pot di- and polysaccharides conversion to highly selective 2,5-dimethylfuran over Cu-Pd/Amino-functionalized Zr-based metal-organic framework (UiO-66(NH2))@SGO tandem catalyst

Abstract

Tandem heterogenous catalysis of bimetallic Cu-Pd on UiO-66(NH2) that were incorporated into sulfonated graphene oxide (Cu-Pd/UiO-66(NH2)@SGO or Cu-Pd/US) was investigated for the one-pot, direct conversion of di- and polysaccharides into 2,5-dimethylfuran (2,5-DMF) without separation of reaction intermediates. In the absence of a homogeneous acidic catalyst, consecutive reactions of glycosidic bond cleavage, isomerization, dehydration, and hydrogenation/hydrogenolysis were preceded by the synergistic effect of a multifunctional Cu-Pd/US catalyst. The strength and ratio of Brønsted and Lewis acid sites by adjusting UiO-66(NH2) to SGO ratios resulted in high-yield 5-(hydroxymethyl)furfural (5-HMF) through sequential glycosidic bond cleavage, isomerization, and dehydration of sucrose. Unlike monometallic Cu and Pd, bimetallic Cu-Pd promoted consecutive COH hydrogenolysis and CO hydrogenation of reaction intermediates, producing 2,5-DMF with a high yield of 73.4% during the one-pot conversion of sucrose at 200 °C and 1 MPa H2 for 3 h. When starch was converted over Cu-Pd/US, 2,5-DMF was formed with 53.6% yield. Direct cellulose conversion into 2,5-DMF with a yield of 29.8% was achieved in the presence of 0.01 M HCl and Cu-Pd/US. The presence of the amino functional group (-NH2) in the UiO-66 framework was beneficial for improving the feed conversion and maintaining catalyst recyclability up to five times with almost no activity loss.