Interfacial Structure-Determined Reaction Pathway and Selectivity for 5-(Hydroxymethyl)furfural Hydrogenation over Cu-Based Catalysts

The catalytic upgrading of biomass-derived feedstocks to valuable chemicals generally requires catalysts with integrated active sites and tuned structures for selective activation of their multifunctional groups. Herein, we fabricated different Cu-based catalysts with multiple interfaces by facile reduction of layered double hydroxides (LDHs), aimed at controlling the reaction pathway and product selectivity in the hydrogenation of 5-(hydroxymethyl)furfural (HMF), an important biomass-based platform molecule. These Cu catalysts were characterized by XRD, Raman, TPR, HAADF-STEM, and in situ XAFS. For Cu/MgAlOx, derived from CuMg5Al2-LDHs, Cu particles were partially encapsulated by a MgAlOx support, thus forming highly intimate Cu-MgAlOx interfaces. On Co@Cu/CoAlOx, derived from CuCoxAl2-LDHs, together with a Cu-CoAlOx interface, partially reduced ultrasmall Co clusters were mounted around Cu particles to form a metallic Co-Cu interface, which is tunable by varying the Cu/Co ratio. As expected, Cu/MgAlO, was only active in C=O hydrogenation to produce 2,5-bis(hydroxymethyl)furan (DHMF) in a 92.7% yield, while Co@Cu/3CoAlO(x) sequentially catalyzed the C=O hydrogenation and C-OH hydrogenolysis to yield as high as 98.5% 2,5-dimethylfuran (DMF), in sharp contrast to Co@Cu/5CoAlO(x), which further broke the C=C bonds of DMF to yield 83.6% 2,5-dimethyltetrahydrofuran (DMTHF). The dependence of the reaction pathway and product selectivity on the composition and properties of the interface was revealed by identifying various intermediates using in situ IR. Specifically, HMF transformed into an O-bound intermediate on the Cu sites over the Cu-MgAlOx, while the unsaturated interfacial Cu-CoAlOx structure served as dual active sites to form a C,O-bound intermediate, thus leading to different products. In addition, the tunable Cu-Co interfacial sites remarkably influenced the adsorption modes of C=C bonds in the furan ring. This work provides a rationale for controlling the reaction pathway and product selectivity for complicated biomass reactions via the controllable construction of multiple interfaces.