Selective activation of the C-O bonds in lignocellulosic biomass for the efficient production of chemicals

The efficient transformation of abundant and renewable lignocellulosic biomass for the production of chemicals and fuels is of considerable importance for establishing a sustainable society. The selective catalytic conversion of the major components of lignocellulosic biomass, including cellulose, hemicellulose and lignin, into key platform chemicals under mild conditions represents an ideal route for the utilization of this abundant resource. Cellulose is composed of multiple glucose units, which are linked together through beta-1,4-glycosidic bonds, and the selective cleavage of these glycosidic bonds would therefore provide access to glucose and glucose derivatives. Hemicellulose is a heteropolysaccharide composed of different sugar units such as glucose, mannose, xylose, arabinose and galactose. The selective cleavage of the glycosidic bonds in hemicelluloses would therefore provide a mixture of different sugars. In contrast to cellulose and hemicellulose, lignin is a complex macropolymer consisting of methoxylated phenylpropane structures. Furthermore, lignin contains a variety of different C-O bond types, including beta-O-4, a-O-4 and 4-O-5 bonds, which connect the primary aromatic units in lignin. The selective cleavage of these C-O bonds would therefore lead to the formation of high-value aromatic compounds. In this review article, we have provided a detailed summary of recent advances towards the development of new catalysts and novel strategies for the selective cleavage of the C-O bonds in cellulose, hemicellulose and lignin, as well as closely related model systems, for the production of glucose, glucose derivatives (including alkyl glucosides, hexitols and gluconic acid), xylose, arabinose and aromatic compounds. The key factors determining catalytic performances have been described in detail. The reaction mechanisms have also been discussed to provide the reader with a deeper understanding of the processes involved in the selective activation of C-O bonds. (C) 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.