Lignin is the largest renewable source of aromatic compounds in nature, and the production of value-added aromatic compounds from lignin can reduce the dependence on fossil fuel feedstocks. Here, a number of unsupported nickel-based catalysts were prepared from the decomposition of nickel formate and were employed for the depolymerization of enzymatic hydrolysis lignin (EHL) in a batch reactor at 280 °C for 6 h with 2 MPa hydrogen in ethanol. Among the samples, Ni (220H) achieved the complete liquefaction of EHL and the highest monomer yield of 28.5%. The results of ¹H-nuclear magnetic resonance (¹H-NMR) and gel permeation chromatography (GPC) studies indicate that the ether linkages were cleaved and the molecular weight of EHL significantly decreased in ethanol without the catalyst, and the Ni (220H) catalyst promoted the depolymerization of EHL and hindered the repolymerization reaction. The para-alkyl side chains of phenolic products are independent of the solvent used, while the structures of aromatic esters are closely related to the solvent used. This work provided a novel and efficient strategy for lignin depolymerization, which is promising for the industrial application of lignin.

中文翻译：

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超临界乙醇中无载体镍催化剂上酶解木质素催化解聚为单体

木质素是自然界中最大的可再生芳香化合物来源，木质素生产增值的芳香化合物可减少对化石燃料原料的依赖。在此，由甲酸镍的分解制备了许多无载体的镍基催化剂，并将其用于间歇式反应器中的酶解木质素（EHL）在280°C下用2 MPa的氢在乙醇中的解聚反应。在样品中，镍（220H）实现了EHL的完全液化，单体收率最高，为28.5％。结果^1个H-核磁共振（¹H-NMR）和凝胶渗透色谱（GPC）研究表明，在没有催化剂的情况下，乙醇中的醚键被裂解，EHL的分子量显着降低，而Ni（220H）催化剂促进EHL的解聚并阻碍了再聚合反应。酚类产物的对烷基侧链与所用溶剂无关，而芳族酯的结构与所用溶剂密切相关。这项工作为木质素解聚提供了一种新颖而有效的策略，对于木质素的工业应用是有希望的。