Study On The Ni-based Catalyst Prepared By Ligand Protection Method In The Hydrogenation Of Lignocellulose

The catalytic reduction and depolymerization of lignin are a hot area in the research of the conversion of lignocellulosic biomass.Current methods mainly use expensive precious metal catalysts,such as Ru,to depolymerize lignin into its monomer compound.Developing alternative catalysts based on non-precious metal can make the process more economically feasible.In this paper,a new type of Ni@C/Al₂O₃ catalyst was prepared by impregnating the Ni（EDTA）^2-anion complex on mesoporous alumina supports with positive charges on the surface.The crystal structure and physicochemical properties of the catalyst were characterized by techniques such as TGA,XRD,XPS,TPR and BET.The results showed that the Ni@C/Al₂O₃ catalyst had a core-shell structure,the core is Ni metal particles,and its surface is covered with a porous N-doped carbon layer.Compared with the Ni/Al₂O₃ catalyst prepared by the conventional impregnation method,the size of the Ni metal particles on the Ni@C/Al₂O₃ catalyst is smaller.Using actual biomass as raw material,the activity of the catalyst in reductive catalytic fractionation of poplar wood chips was investigated.The results showed that the total yield of monomer products on the Ni@C/Al₂O₃ catalyst reached 34.5%,while on the Ni/Al₂O₃catalyst was only 25.9%.The effects of the preparation conditions such as the catalyst reduction temperature,the loading of Ni metal,the molar ratio of EDTA and Ni on the catalytic reduction and depolymerization of poplar wood chips were further investigated.The final optimized recipe adopted a reduction temperature of 500℃,a Ni loading of 28 wt%,and a molar ratio of EDTA to Ni at 1:1.The high activity of the Ni@C/Al₂O₃ catalyst can be attributed to the sparse distribution of Ni metal particles and the protective effect of the carbon layer.Similarly,the chelation of Ni metal particles and EDTA ligand had a significant effect on the product selectivity of the hydrogenation reaction of the model compound,i.e.,4-propylguaiacol.The product catalyzed by Ni/Al₂O₃ is mainly 4-propylcyclohexane,while some4-propylcyclohexanol was also produced when using the Ni@C/Al₂O₃ catalyst.