纳米氧化铕催化氧化木质素制备芳香化合物的研究

A Study on the Catalytic Oxidation of Lignin and Preparation of Aromatic Compounds by Europium Oxide

摘要: 木质素是唯一大规模可再生的芳香化合物来源，同时具有不可食用、来源广泛和价格低廉等优势。定向催化氧化解聚木质素可以得到用途广泛的芳香醛、酸、酯类化合物。催化剂是定向催化解聚木质素的关键，稀土氧化物在催化氧化反应中表现出独特的性质，但是纳米稀土氧化物在木质素的多相催化解聚的性能鲜见报道。本文采用水热法制备了纳米颗粒氧化铕(Eu₂O₃)催化剂，首先对木质素模型分子2-(2,6-二甲氧基苯基)-1-苯乙醇(dp-ol)进行了催化氧化，得到了最佳催化条件(220℃，1 MPa氧气，50%的甲醇水溶液，4小时)和最高转化率(72.24%)。GC-MS检测主要产物为苯甲酸、苯甲酸甲酯、苯乙酮，证明木质素模型分子中的β-O-4键和C_α-C_β键均发生了断裂。其次使用该催化剂对真实木质素进行催化氧化解聚，得到主要产物为丁二酸二甲酯、2-甲氧基丁二酸二甲酯、均苯四甲酸四甲酯等产物。纳米Eu₂O₃颗粒催化剂易于制备，价格低廉，具有良好的研究价值与应用前景。

Abstract: Lignin is the only resource of large-scale renewable aromatic compounds, which are inedible, widely available, and inexpensive. Directional catalytic oxidation and depolymerization of lignin can provide various aromatic compounds such as aromatic aldehydes, acids and esters. The catalyst plays a key role in directional catalytic depolymerization of lignin. Rare earth oxides exhibit unique properties in catalytic oxidation reactions, but the performance of nano-rare earth oxides in heterogeneous catalytic depolymerization of lignin has rarely been reported. In this paper, na-nometer europium oxide (Eu₂O₃) catalyst was prepared by the hydrothermal method. Firstly, the lignin model molecule 2-(2, 6-dimethoxyphenyl)-1-phenylethanol (dp-ol) was catalyzed by nano-Eu2O3; the optimum catalytic conditions (1MPa oxygen, 50% methanol aqueous solution, 4 hours) and the highest conversion (72.24%) were obtained. The main products detected by GC-MS were benzoic acid, methyl benzoate and acetophenone, which proved that the β-O-4 bond and C_α-C_β bond in lignin model molecule were broken. Secondly, the catalyst was applied in the catalytic oxidative depolymerization of real lignin; the main products were dimethyl succinate, dimethyl 2-methoxysuccinate, tetramethyl homophenyltetracarate. In this paper, nano-Eu₂O₃ particulate catalyst exhibited excellent catalytic performance, and this catalyst is easy to prepare for a low price. Therefore, nano-Eu2O3 particle catalyst has good research value and application prospect.