Shi Qiu,Xuan Guo,Yong Huang,Yunming Fang,Tianwei Tan
Graphical Lignin first : A flexible lignin-first biorefinery could be developed by task-specific catalyst design for hemicellulose retention or feedstock extension. Mo x C/carbon nanotube (CNT) is found to be a promising catalyst for the retention of hemicellulose by cleavage of the bonds between lignin and carbohydrates with high selectivity. Ru/CMK-3 achieves the extension of the feedstock for the lignin-first biorefinery from hardwood to softwood. A catalytic reductive fractionation method for lignocellulosic biomass, termed lignin-first biorefinery, has emerged, which emphasises preferential depolymerization of the protolignin. However, in most studies, the lignin-first biorefinery is only effective for hardwood that has a high syringyl/guaiacol (S/G) ratio of lignin building blocks, and the degradation of hemicellulose also takes place simultaneously to a certain degree. In this study, two task-specific catalysts were developed to realize hemicellulose retention and feedstock extension through the development of an objective performance–structure relationship. It is found that Mo x C/carbon nanotube (CNT) is highly selective in the cleavage of bonds between carbohydrates and lignin and ether bonds in lignin during the catalytic reductive fractionation of hardwood, leading to a carbohydrate (both cellulose and hemicellulose) retention degree in the solid product close to the theoretical maximum and a delignification degree as high as 98.1 %. Ru/CMK-3 is demonstrated to be effective in the catalytic reductive fractionation of softwood and grass, resulting from its weak acidity and high mesoporosity.
At near ambient temperature, Ru nanoparticles entrapped in ordered mesoporous carbons (OMCs) CMK-3 show superior efficiency in the green reduction process of nitrobenzene and its derivatives with hydrazine monohydrate as a hydrogen donor using water as solvent. The Ru/CMK-3 catalyst exhibited much higher activity than a commercial Ru/C catalyst purchased from Alfa Aesar toward the reduction of nitrobenzene with hydrazine monohydrate under the same conditions. The interaction of Ru nanoparticles with CMK-3 and the mesoporous structure of CMK-3 OMCs might play important roles in determining the catalytic performance of the Ru/CMK-3 catalyst. In addition, the catalytic performance of the Ru/CMK-3 catalyst for the reduction of nitrobenzene was also compared using different hydrogen sources. Hydrazine monohydrate was found to be suitable as a hydrogen donor for the reduction of nitrobenzene and its derivatives. Compared with those obtained in the reduction of nitrobenzenes using 4.0 MPa hydrogen, the catalytic activity of the Ru/CMK-3 catalyst obtained using hydrazine monohydrate as hydrogen donor was much higher in most cases.
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