Hydrogenation Of Lignin-derived Oxygenated Compounds By Ni-based Catalysts

Lignin is the most abundant biomass resource of natural aromatic compounds and has great potential for producing high value-added aromatic chemicals.Lignin is an underutilized carbon resource,and its efficient utilization is a current research hotspot.However,due to its irregular molecular structure and its thermal and chemical resistance to degradation,selective depolymerization of lignin into derivative monomers remains a difficult challenge.Catalytic hydrodeoxygenation is one of the most effective methods to convert lignocellulosic biomass.Most of the current lignin hydrodeoxygenation conversion processes use precious metal catalysts,and their high cost is a major obstacle for practical industrial applications.In this paper,a method of pyrolyzing metal complexes was used to prepare an effective and inexpensive nickel-based catalyst supported by activated carbon.Guaiacol was used as a typical model compound monomer of lignin to investigate the hydrodeoxygenation performance of the catalyst.The main products of Ni/C catalyst prepared by traditional impregnation methods and precious metal Ru/C catalyst are cyclohexanol and cyclohexanediol.However,The main product of the guaiacol hydrodeoxygenation reaction with Ni/C catalyst prepared by pyrolytic metal complex method is phenol.The activity of the catalyst prepared with disodium ethylenediamine tetraacetate as a ligand is close to that of precious metal catalysts.When the reaction temperature is 280℃,the conversion rate of guaiacol reaches 94%.The performance was close to that of precious metal catalysts.The hydrogen pressure affects the selectivity of the product: when the hydrogen pressure is 1.6 MPa,the selectivity of phenol can reach 70%.The reaction mechanism is simply speculated that guaiacol is firstly hydrogenolyzed,the C-O bond is broken to demethoxy or methyl to generate phenol or catechol,and then the benzene ring is hydrogenated to form cyclohexanol or cyclohexanediol.XRD and BET techniques were used to characterize the nickel-based catalysts prepared with different complexes.As a result,it was found that the degree of dispersion of the metallic nickel active component on the surface of the supporting activated carbon was very different.