Catalytic Hydrolysis/Hydrogenolysis of Lignin-Derived Aryl Ethers over Bimetallic Pd-Ni Systems: The Directional Regulation of Reaction Pathways

Directional regulation for the reaction pathways of lignin-related compounds represents a meaningful process for obtaining value-added chemicals. Herein, a series of Pd-based, Ni-based, and Pd-Ni catalysts were used to investigate the conversion pathways of the lignin-derived aryl ethers. It was found that Pd-based catalysts easily induced partial hydrogenation-reductive hydrolysis of diphenyl ether (DPE), while DPE underwent direct hydrogenolysis and partial hydrolysis over Ni-based catalysts. DPE was converted to high-yield cyclohexanol by direct catalytic hydrolysis/hydrogenolysis over a bimetallic Pd-Ni catalyst. 3%Pd-1%Ni/AC exhibited superior performance that outperformed the monometallic catalysts (1%Ni/AC and 3%Pd/AC) and mixed 1%Ni/AC and 3%Pd/AC under the equal conditions. The characterization results revealed that electron transfer from Pd to Ni, led to a strong interaction between Pd and Ni. The electronic deficient Pd possessed optimized H2 activation ability, and the inserted Ni was conducive to the cleavage of DPE. The deuterium experiment and reaction kinetic study demonstrated that DPE was cleaved to 75.7% cyclohexanol via catalytic hydrolysis/hydrogenolysis over 3%Pd-1%Ni/AC. Besides, other lignin-related compounds could also be converted into high-value-added chemicals over 3%Pd-1%Ni/AC by cleaving the C–O bond.