| 内容提要: |
Lignin has been proposed as one of the most important renewable feedstock as it could potentially be used to prepare functionalized aromatic fine chemicals. The critical point for the lignin transformation lies in theselective cleavage of C-O and C-C bonds, whilst suppressing hydrogenation of the aromatic. In this work, CoAl hydrotalcite-derived MoS2/Co9S8-Al2O3 catalyst was prepared and employed in the hydrodeoxygenation (HDO) of diphenyl ether (4-O-5 linkage). According to the characterization results of HRTEM, the sulfide species were highly dispersed, which could be ascribed to the atomic-scale dispersion of metal cations and the anchoring effect of the substrate in CoAl hydrotalcite precursor. After optimization of the reaction conditions, the MoS2/Co9S8-Al2O3 catalyst achieved an equivalent benzene yield (carbon yield) of 83.0%, accompanied by few aromatic ring over hydrogenation product, under 3 MPa H2 (measured in RT), 265 °C for 10 h. Interestingly, the subsequent reusability tests showed that the catalyst possess stable activity over 10 runs, and the benzene yield increased to around 87.0% and less over hydrogenation products were generated. The characterization results of XRD, XPS, ICP, Raman and TEM presented that no obvious structural changes occurred in the catalyst except for partial oxidation.
We proposed that it is the oxidation of the catalyst caused by the generated water during the reaction inhibit its hydrogenation ability, which leads to a higher yield of benzene. Additional experiments with adding water to the reaction system were carried out to explore the specific effects of water. Results shows that appropriate water can improve the benzene yield to 96.8% with the Co9S8 species translate to cobaltous sulfate phase in the catalyst. In the substrates extension studies, the catalyst also showed high activity and selectivity to cleave the different type of C-O bonds to form aromatic products. In the conversion of realistic lignin, the catalyst showed excellent activity in the hydrogenolysis of major linkages such as β-O-4，α-O-4 and β-β between aromatic units. |