Construction Of Nitrogen-doped Carbon Supported Ni Catalyst And Its Application In The Production Of Phenolic Monomers From Lignin Hydrogenolysis

Lignin has the characteristics of green,clean,and sustainable regeneration,and is considered the best choice to replace fossil fuels in the production of high value-added chemicals.However,the complex chemical structure and stable linkages of lignin make it difficult to degrade effectively.Catalytic hydrogenolysis has attracted widespread attention due to its excellent carbon utilization efficiency and relatively simple product distribution,making it one of the most effective methods for lignin depolymerization.The development of efficient and stable catalysts that selectively break the C-O bonds in lignin is of great significance for the conversion of lignin into high-value aromatic compounds.To address the drawbacks of low catalytic activity and easy loss of metal components during lignin hydrogenolysis,this study employs a simple in-situ pyrolysis approach using a mixture of metal salts and carbon-nitrogen precursors to prepare a nitrogen-doped carbon-supported Ni catalyst for lignin hydrogenolysis to produce phenolic monomers.The specific research carried out in this study is as follows:（1）Direct pyrolysis of nickel acetate and melamine composite enables the synthesis of nitrogen-doped carbon nanotube-supported Ni nanoparticles（Ni/NCNT10-800）through a two-step pyrolysis process.The influence of melamine loading and pyrolysis temperature on the morphology and catalytic performance of the catalyst is analyzed using characterization techniques such as SEM,TEM,XRD,XPS,and BET to investigate the physicochemical properties of the catalyst.The results indicate that melamine plays a critical role in the formation of carbon nanotube structures,while the Ni-Nx bonds formed between doped N and Ni serve as anchoring sites for the metal,promoting the dispersion of Ni nanoparticles.The formation of Ni-Nx enhances the electronic interaction between the metal Ni and the nitrogen in the support,thereby improving the catalytic activity and dissociation capacity of hydrogen.The catalyst exhibits excellent activity in lignin hydrogenolysis experiments,achieving a phenolic monomer yield of 23.1%under mild conditions in isopropanol solution（280℃,3 h,1MPa H₂）.After five cycles,the catalyst retains its structural and physicochemical properties without significant changes,indicating its strong stability.（2）Direct pyrolysis of glucose,melamine,and nickel acetate composites is employed to prepare a nitrogen-doped carbon nanosheet-supported Ni catalyst（Ni@NC-800）.The oxygen-functional groups on the surface of glucose molecules exhibit chelating effects with Ni ions,while melamine and glucose form layered nitrogen-doped carbon and aromatic carbon frameworks,respectively,during low-temperature pyrolysis,inhibiting the growth of Ni nanoparticles.During high-temperature pyrolysis,the instability of nitrogen-doped carbon leads to the incorporation of nitrogen radicals into the aromatic carbon framework,and the corrosive gas produced from the decomposition of nitrogen-doped carbon etches the carbon support,resulting in a high surface area and well-developed three-dimensional porous structure of the carbon-nitrogen support,thereby enhancing mass transfer rates during hydrogenolysis.DFT calculations demonstrate that nitrogen-doped carbon-supported Ni nanoparticles exhibit more effective adsorption of reactant molecules and promote the cleavage of C-O bonds compared to pure carbon-supported Ni nanoparticles.Birch lignin hydrogenolysis experiments were conducted to investigate the effects of reaction temperature,time,and hydrogen pressure on the production of phenolic monomers.The degradation products were analyzed using GC-MS and 2D HSQC.The results demonstrate complete lignin depolymerization under the optimal reaction conditions（260℃,3 h,1 MPa H₂）,with a high phenolic monomer yield...