生物催化串联P-NiMoS/Al2O3多相催化用于木质素加氢解聚研究

With the rapid development of the cellulosic ethanol industry, a large amount of lignin waste has been produced and has not been effectively utilized. Selective production of phenolic compounds by hydrodepolymerization of lignin is a promising method for lignin valorization. Cleavage of β-O-4 ether bond in lignin dimer model compound via a dehydroxylation-hydrogenation strategy is highly efficient. However, chemical oxidation by chemical reagents will inevitably lead to lignin repolymerization, resulting in failure of this strategy. In this project, a natural non-radical selective degradation biological system was introduced. Cα-dehydrogenase LigD expressed from Sphingobium sp. Strain SYK-6 was used to selectively oxidize Cα-OH in β-O-4 ether bond of lignin to Cα=O without causing repolymerization of lignin. At the same time, P-NiMoS/Al2O3 catalyst was prepared to catalyze lignin which was preferentially oxidized by Cα-dehydrogenase LigD. The additive P was introduced to enhance the dispersity of Ni-Mo-S active phase and promote the synergistic catalysis of the Ni-Mo bimetal. Thus the acidity, hydrogenation site and redox site was regulated to inhibit the reduction of Cα=O during hydrodepolymerization reaction, promoting direct deoxygenation of lignin to form monophenolic compounds. The combination of biocatalytic and P-NiMoS/Al2O3 treatment steps provides new ideas and approaches for the value-added utilization of lignin waste.

随着纤维素乙醇工业的迅猛发展，产生了大量木质素废弃物且未进行有效利用。木质素加氢解聚制备单酚是研究较多且较有前景的木质素增值方法。优先将木质素二聚体Cα-OH氧化为Cα=O再进行加氢解聚是一种高效的木质素解聚策略，然而化学试剂氧化过程不可避免会引起木质素再聚合，导致该策略应用在木质素大分子时失效。本项目采用交叉学科的研究方法，引入天然的非自由基选择性降解生物系统，采用Sphingobium sp．Strain SYK-6表达的Cα-脱氢酶LigD对Cα-OH位点进行定向氧化改性且不引起木质素的再聚合。同时，制备P-NiMoS/Al2O3催化剂，通过助剂P调控Ni-Mo-S活性相在催化剂表面的分布，促进Ni-Mo双金属协同催化，改善催化剂表面的酸性，调控其加氢位点和氧化还原位点，抑制加氢解聚反应中Cα=O的还原促进木质素直接脱氧断裂生成单酚类化合物，为木质素废弃物增值利用提供新的思路和途径。

木质素是世界上唯一一种大量存在的由芳香类化合物组成的可再生原料，优先将木质素二聚体Cα-OH 氧化为Cα=O再进行加氢解聚是一种高效的木质素解聚策略，然而化学试剂氧化过程不可避免会引起木质素再聚合，导致该策略应用在木质素大分子时失效。因此，构建温和的Cα催化氧化体系且不引起木质素聚合，有助于揭示“预氧化&加氢解聚”两步策略对大分子木质素解聚的机制和关键影响因子。.首先，我们从白腐真菌Physisporinus vitreus和木质素降解细菌 Sphingobium sp. SYK-6分别提取和诱导表达了木质素酶漆酶（Pv-Lac）和Cα脱氢酶（LigD），并且以木质素模型化合物和大分子木质素为研究对象，探究了木质素分别经Pv-Lac和LigD催化氧化后的结构变化。研究发现，反应体系pH为7时，Pv-Lac对木质素二聚体的催化氧化主要以解聚和Cα-OH氧化为主，而酸性体系下会引起木质素的重聚合。紧接着，我们以大分子木质素为研究对象，发现Pv-Lac可使其Cα-OH氧化程度提高18%，缩合度降低且不引起木质素的聚合。而大分子木质素经LigD氧化后，Cα-OH氧化程度可提高45%，远高于漆酶的催化氧化性能，并且未引起木质素的聚合。经Pv-Lac和LigD催化氧化的木质素分别经过P-NiMoS/Al2O3催化加氢解聚后，木质素油产率均得到了提升，其中单体收率分别提升至41%和70%。此外，研究发现，与NiMoS/Al2O3催化剂相比，P改性的P-NiMoS/Al2O3催化剂可大大提高氧化型木质素的加氢解聚效率。.综上，我们构建了温和高效的 “酶催化氧化&加氢解聚”体系，LigD可对木质素Cα-OH进行高效氧化改性且不引起木质素的再聚合，且酶改性木质素经加氢解聚后，木质素油和木质素单体收率均得到了大幅提升，为木质素废弃物增值利用提供了新的思路和途径。