Mechanisms of Caromatic-C bonds cleavage in lignin over NbOx-supported Ru catalyst
Mechanisms of Caromatic-C bonds cleavage in lignin over NbOx-supported Ru catalyst
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NbOx 负载 Ru 催化剂上木质素中芳香族 C 键断裂的机制
DOI：
10.1016/j.jcat.2021.01.001
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发表时间：
2021-01-25
影响因子：
7.3
通讯作者：
Wang, Yanqin
中科院分区：
文献类型：
--
作者：
Dong, Lin;Xia, Jie;Wang, Yanqin
有效且选择性地切割木质素中的C-芳香族-C键以提高单环芳烃的生产率是一项极具挑战性且有吸引力的任务。之前，我们报道了一种Ru/NbOPO 4催化剂，其在一锅法木质素转化中实现了单元间C-C和C-O键的催化裂解[Chem，2019，5，1521-1536]。然而，NbOx物种在选择性C-芳族-C裂解中的作用尚不清楚，需要广泛研究。本文通过与Ru/TiO_2、Ru/ZrO_2和Ru/Al_2O_3催化剂的比较，着重探讨了NbOx负载Ru催化剂上C-芳香-C键断裂的催化机理。结果表明，Ru/Nb_2O_5催化剂具有较高的活性和对单环烃的选择性。结合漫反射红外傅里叶变换光谱（DRIFTS）和密度泛函理论（DFT）计算分析明确证实：（i）NbOx不仅能通过苯环强吸附苯基环己烷，而且能选择性地活化苯环与环己烷之间的C-芳香-C键;和（iii）NbOx可以显著降低碳阳离子中间体（C6 H5（H）C6 H11+）的C-芳族-C键断裂的势垒。初步建立了详细的反应机理，为设计新型高效催化剂提供了理论依据。(C)2021爱思唯尔公司All rights reserved.
Efficient and selective cleavage of C-aromatic-C linkages in lignin to enhance the productivity of monocyclic aromatic hydrocarbons is an extremely challenging and attractive task. Previously, we reported a Ru/NbOPO4 catalyst that realized the catalytic cleavage of both interunit C-C and C-O bonds in one-pot lignin conversions [Chem, 2019, 5, 1521-1536]. However, the roles of NbOx species in the selective C-aromatic-C cleavage are not clear and need to be extensively studied. Herein, we focus on the exploration of the catalytic mechanisms of C-aromatic-C bond cleavage over NbOx-supported Ru catalyst, by comparing with those of Ru/TiO2, Ru/ZrO2, and Ru/Al2O3 catalysts. It shows that the Ru/Nb2O5 catalyst exhibits high activity and remarkable selectivity to monocyclic hydrocarbons. A combined diffuse reflectance infrared Fourier Transform spectra (DRIFTS) and density functional theory (DFT) calculation analysis unambiguously confirmed that (i) NbOx not only can strongly adsorb phenylcyclohexane via benzene ring, but also selectively activate C-aromatic-C bond between benzene ring and cyclohexane; (ii) NbOx can promote the protonation of phenylcyclohexane with the assistance of H3PO4; and (iii) NbOx can significantly reduce the barrier of C-aromatic-C bonds cleavage of the carbocation intermediate (C6H5(H)C6H11+). A detail underlying mechanism has been established, which would have further implications to promote the design of new, high efficient catalysts. (C) 2021 Elsevier Inc. All rights reserved.