Task-Specific Catalyst Development for Lignin-First Biorefinery toward Hemicellulose Retention or Feedstock Extension

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.