Charge-separated metal-couple-site in NiZn alloy catalysts towards furfural hydrodeoxygenation reaction

Catalytic conversion of biomass furfural (FAL) to high value-added products (e.g., 2-methylfuran, MF) has attracted considerable attention, in which control over catalytic selectivity plays a crucial issue. Herein, a series of heterogonous NiZn alloy supported on the mixed metal oxides (MMO) were synthesized derived from layered double hydroxides (LDHs) with various Ni/Zn ratio (3/1, 1/1 or 1/3). XRD, HRTEM and XAFS measurements confirm that with the increase of Zn content, the corresponding NiZn alloy transforms from α-NiZn (Ni3Zn1-MMO and Ni1Zn1-MMO) to β-NiZn (Ni1Zn3-MMO). Dramatically, the selectivity of MF displays an improvement from 12% to 95% along with this phase transformation process; and the MF yield reaches to 95% over Ni1Zn3-MMO sample. A combination study including XPS, CO-DRIFTS, in situ FT-IR and DFT calculation verifies that metallic Ni serves as active site, resulting in an effective suppression of side reactions (furan ring hydrogenation). Moreover, a charge-separated metal-couple-site (Niδ--Znδ+) is on the surface of Ni1Zn3-MMO originating from electron transfer between Ni and Zn. This active structure stabilizes a η2(C, O) adsorption configuration of intermediate, in which C atom is bonded to the Niδ− site and O atom is attached to the Znδ+ site. Then, this adsorption configuration facilitates the CO cleavage, giving rise to the production of MF. This work provides an efficient and cost-effective catalyst that can simultaneously inhibit CC hydrogenation and promote CO cleavage, which would be potentially used in catalytic conversion of biomass-derived platform molecules.