Shuai Xu,Qi Gao,Ziyan Hu,Yitong Lu,Yanlin Qin,Yuliang Li
The selective breaking of the Cβ–O bond has great potential for the conversion of lignin into high-value aromatic monomers. In the present work, we designed a CdS–SH/TiO2 heterojunction photocatalyst for the efficient selective breaking of the Cβ–O bond. The surface modification of CdS by –SH promoted close contact between the catalyst and lignin and further promoted the Fermi level matching with TiO2. A type-II heterojunction was constructed by CdS–SH and TiO2 nanosheets to enhance the light absorption range and further increase the separation of photogenerated electron–hole pairs, resulting in high catalytic activity. Finally, 85% phenol and 87% acetophenone yields were obtained under mild light irradiation using 2-phenoxy-1-phenylethanol as the model substrate. Several control experiments, along with DFT calculations, indicate that the reaction pathway is more likely to involve the oxidation of Cα–OH to form Cα═O initially, followed by the activation of Cβ–O, which is then reduced to further form aromatic monomers. This work achieves the efficient selectivity of lignin depolymerization and provides a reference for the design of heterojunction photocatalysts in the valorization of lignin.
Fa-Peng Wu,Le-Le Qiu,Yun-Peng Zhao,Zong-Pin Fu,Jing Liang,Jian Xiao,Jian Li,Fang-Jing Liu,Jing-Pei Cao
Hydrogenolysis of β-O-4 linkages in lignin to produce aromatic compounds is attractive but challenging. Currently, external hydrogen source like hydrogen gas or hydrogen-donor solvent is necessary during hydrogenolysis, leading to high cost and low selectivity of products. Herein, a NiCu/Al 2 O 3 catalyst was prepared for self-hydrogen transfer hydrogenolysis (SHTH) of C β -O bond using inherent C α H-OH structure as H-source. A β-O-4 model compound, 2-phenoxy-1-phenethanol, was completely transformed into acetophenone and phenol at 220 ℃ under 1 MPa N 2 for 2h. The SHTH reaction proceeded through a dehydrogenation reaction followed by a hydrogenolysis reaction. Hydrogen radicals released from C α H-OH group generated a “hydrogen pool” on the catalyst surface, which inserted into the formed β-O-4 ketone intermediate to cleave the C β -O bond. The catalyst presented outstanding reusability and universality during the SHTH reaction. Moreover, the methoxy groups at aryl positions impeded the SHTH process, and the steric effect was related to the amount and position of methoxy groups. This study realizes the utilization of structural hydrogen from lignin model compounds for its C β -O bond cleavage , providing an economical and sustainable method toward lignin valorization.
Jifang Zhang,Chengcheng Suo,Jinde Sun,Wei Li,Sha Luo,Chunhui Ma,Shouxin Liu
In this study, C α –C β and C β –O bond cleavage of β-O-4 model compound (2-phenoxy-1-phenylethanol) were accomplished by electrocatalysis depolymerization process in deep eutectic solvents (DES) systems. We have investigated the application of Ni-Co/C catalysts on working electrode, which were synthesized with impregnation method. The Ni-Co/C with porous structure and abundant active sites, was shown an excellent electrocatalysis activity. Specific structure of Ni-Co/C could provide greatly efficient adsorption and desorption capacity to promote C α –C β and C β –O bond cleavage. Therefore, in this electrocatalysis depolymerization process, the highest depolymerization rate exceeded 90%. And the yields (and conversion rates) of products (including benzaldehyde, acetophenone, benzoic acid, phenol) can reach to 124.08 mg/g (25.05%), 23.29 mg/g (4.15%), 44.64 mg/g (7.83%), 30.3 mg/g (6.9%). Furthermore, the electrocatalysis mechanism of C α –C β and C β –O bond was investigated. The cleavage of C α –C β and C β –O bond was initiated by in situ generated free radicals through Ni-Co/C. Then, the cleavage of C α –C β and C β –O bond were occurred by ·OH and ·O 2 − . The results were showed that the C α –C β bond cleavage was more in line with the β-C elimination and free radical pathways, and C β –O bond cleavage was consistent with direct oxidative addition. The enhanced electrocatalytic efficiency of the low-cost Ni-Co/C electrocatalyst combined with its good chemical stability and selectivity, which offer a promising route for developing an efficient lignin depolymerization technology.
危险品化学品经营许可证（带存储）