Study On The Reaction Of Nickel-based Catalysts In Selectively Breaking Aryl Ether Bonds

Lignin is an aromatic renewable resource in nature.Selective cleavage of aryl ether bonds is a necessary reaction in the lignin valorization,and also one of the important ways to build the efficient lignin depolymerization system.In this paper,the Al-SBA-15 mesoporous materials with well controlled acid amount were prepared via a postsynthesis method,and the highly dispersed NiO_x/Al-SBA-15 catalysts were obtained by a urea precipitation method.The catalytic reaction system of selective cleavage of aryl ether bonds in guaiacol was set up with mild conditions,the guaiacol and lignin depolymerized oils could be converted into phenols in this reaction system.The main research contents are as follows:1.The incorporation of Al species into SBA-15 framework by a postsynthesis method can generate Lewis acid sites which can increase the acidity and enhance the metal-support interaction.The highly dispersed NiO_x/Al-SBA-15 catalysts could be obtained by a urea precipitation method which showed a high reaction activity in selective cleavage of aryl ether bonds in guaiacol at 120 ^oC,0.1 MPa H₂ in water solvent.The guaiacol conversion,phenol selectivity and the carbon balance was 79.8%,69.8%and 81.2%,respectively.With the increase of the acid amount on the surface of the catalyst,the guaiacol conversion was gradually increased,the phenol selectivity was increased first and then decreased,and the carbon balance was decreased.The guaiacol could polymerized to form non-volatile macromolecular compounds over a catalyst with high surface acid amount,which lead to a low carbon balance.2.The effect of initial hydrogen pressure,reaction temperature and reduction temperature of the catalyst?the valence state of nickel?on the reaction of cleavage of aryl ether bonds in guaiacol were investigated over the NiO_x/Al-SBA-15?Si/Al=10?catalyst.With the increase of initial hydrogen pressure,the guaiacol conversion and cyclohexanol selectivity were gradually increased,while the phenol selectivity was decreased.With the increase of reaction temperature,the guaiacol conversion was gradually increased.3.Catalytic cleavage of aryl ether bonds in lignin based oils could be realized in120°C and 2 MPa H₂ in water over NiO_x/Al-SBA-15?Si/Al=10?catalyst,which could produced phenol,ethyl phenol,hexanol and cyclohexanol.The total selectivity of phenols in this system was up to 59.8%?...