Preparation Of Carbon-Supported Ni-Based Catalysts And The Catalytic Study On The Cleavage Of C-O Bond Of Lignin

It has become a global consensus to seek renewable and sustainable alternative resources with the overexploitation of fossil resources.In the main three chemical depolymerization(pyrolysis,reduction and oxidation)of lignin,the catalytic oxidation depolymerization is favored because of its low energy consumption and mild conditions required to achieve high enough conversion.However,the recalcitrance and heterogeneity of lignin frequently generated the complexity of oxidation depolymerization products.Generally,oligomers(lignin model compounds)containing representative lignin bonds were employed to reveal the cleavage mechanism of bonds.The compatibility between of the porous MOF material and the catalyst encouraged the employment of the metal-based MOFs catalyst in the lignin high-valued technology.In this paper,it was prepared that a series of Ni-based monometallic or bimetallic catalysts for the oxidation depolymerization of the β-O-4 bond in lignin and lignin dimers to liquid fuels and high-valued chemicals.The influence of different metal combinations and different metal ratios on the physical and chemical properties of catalyst were investigated in detail.And the influence of catalyst type,reaction temperature,oxygen pressure,reaction time and solvent system on the catalytic conversion of β-O-4 model compounds and lignin were investigated.The specific contents are shown as follows:1.It was prepared that a series of monometallic(Ni,Co,Cu)MOFs catalysts by hydrothermal method with Ni(NO3)2·6H2O as metal source and trimesic acid(BTC)as the template for the catalytic conversion of the lignin β-O-4 model compound 2-phenyl1-acetophenone.The physicochemical properties of the catalysts were analyzed by XRD,SEM,TEM,NH3-TPD and XPS.It was found that the Ni/C-10 catalyst showed good dispersion and regular spherical structure with around 29.88 nm particle size distribution and 5.9 mmol/g acid amount.The Ni0 of the catalyst played an important role in the catalytic selective oxidation conversion of 2-phenoxyl-1-acetophenone to phenol and benzoic acid.The selectivity of phenol was increased to more than 70%by Ni/C-1 0 catalyst,which showed a good recovery,with the optimal conditions,namely,the substrate dissolved in methanol was heated to 160℃ and maintained for 4 h after pressurizing originally with oxygen to 0.5 MPa.2.It was prepared that a series of bimetallic MOFs catalysts by hydrothermal method with the introduction of a second metal(Co,Cu,Mo)into the Ni-based catalyst for the catalytic conversion of the lignin β-O-4 model compound 2-phenyl-1acetophenone.The effects of three different ligands,namely,Trimesic acid(BTC),pPhthalic acid(PTA)and 2,5-Dihydroxyterephthalic acid(DHTA),on the catalytic activity were further investigated.The physical and chemical properties of the catalyst were analyzed by XRD,SEM,TEM,NH3-TPD and XPS.It was found that the introduction of Mo had a positive effect on the dispersion of Ni and the unity of crystal form.The Ni3C was reduced to Ni0 and the metal particle size was reduced to about 17 nm.A methanol-tetrahydrofuran cosolvent was explored to assist the oxidation depolymerization of 2-phenyl-1-acetophenone by Ni4Mol/C-BN catalyst,which showed an improving recovery,and the mechanistic insights were discussed.3.The monometallic catalyst Ni/C-10 and the bimetallic catalyst Ni4Mol/C-BN that performed well in the oxidation conversion of lignin model compounds were applied to the catalytic depolymerization of real lignin.The Ni4Mo1/C-BA catalyst calcinated on air atmosphere was also added to the comparison,which confirmed that air calcination cannot play a positive role on the catalytic activity of Ni-based catalyst in the oxidation conversion of lignin.The lignin(enzymatic lignin,Kraft lignin and alkali lignin)extracted with different technology were investigated as substrates for the universality and practicability of Ni-based catalyst in the catalytic oxidation of real lignin.The degree of depolymerization and the distribution of products were analyzed by the element analysis,GPC and GC-MS.It was found that the products obtained by the selective depolymerization of lignin with different extraction technology on the Nibased catalytic systems were mainly guaiacyl(G)aromatic monomers.Additionally,the largest component was all vanillin in the aromatic products from the oxidation depolymerization of lignin with various extraction technology by different Ni-based catalysts.