Catalytic valorization of biomass and bioplatforms to chemicals through deoxygenation

Catalytic valorization of biomass as a renewable resource into building-block chemicals or synthetic intermediates would contribute to establishing a sustainable chemical industry. Because of the high oxygen content in lignocellulosic biomass, it is necessary to develop methods and systems to remove specific oxygen atoms selectively from the biomass or biomass-derived platform compounds (bioplatforms) to produce value-added chemicals that can be directly used in the chemical industry. This review highlights advances in the past decade in the catalytic valorization of biomass and bioplatforms to a variety of chemicals by deoxygenation. Emphases are put on the selective cleavage of specific C-O bonds of cellulose, the most abundant component in lignocellulosic biomass, furanic and phenolic compounds that can be derived from hemicellulose and lignin to form ethanol, adipic acid, 1,6-hexanediol, methyl furan, dimethyl furan, p-xylene and arene products. Since multiple C-OH bonds exist in biomass and bioplatforms, this review analyzes different strategies that can be exploited to remove one or more -OH groups to offer ethanol or adipic acid. Furanic compounds have both C-O-C bonds in furan ring and C-OH/C =O bonds connected to the ring, and thus the cleavage of different C-O bonds can lead to either linear or aromatic products. The methods and catalytic systems for the transformations of furanic compounds such as 5-hydroxymethylfurfural and furfural to 1,6-hexanediol, methyl furan, dimethyl furan and p-xylene are summarized. The deoxygenation of lignin-derived phenolic compounds to arene products by hydrogenolysis is briefly described. This review also highlights recent advances in understanding the reaction mechanisms for deoxygenation of biomass and bioplatforms. Key factors determining the product selectivity as well as activity will also be discussed.