The catalytic conversion of cellulosic biomass to downstream products provides a viable solution to alleviate the energy crisis and global warming. This article provides a relatively comprehensive review of the dehydration of glucose (the monomer of cellulose) and fructose considering various catalyst and solvent systems. Biphasic solvents and heterogeneous systems are recommended from the point of view of industrial applications. A two‐step catalytic conversion of glucose via fructose has been envisaged: first, isomerization of glucose to fructose, which has been extensively discussed in this review, and then transformation of fructose to downstream products. Two‐step tandem catalytic reactions from glucose to downstream products (i.e., one‐pot synthesis via fructose) are also attractive for industrial applications and should be given more attention. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd

Ab initio and density functional calculations are conducted to investigate the radicalization processes and radical catalysis of biomass sugars. Structural alterations due to radicalization generally focus on the radicalized sites, and radicalization affects H-bonds in D-fructofuranose more than in D-glucopyranose, potentially with outcome of new H-bonds. Performances of different functionals and basis sets are evaluated for all radicalization processes, and enthalpy changes and Gibbs free energies for these processes are presented with high accuracy, which can be referenced for subsequent experimental and theoretical studies. It shows that radicalization can be utilized for direct transformation of biomass sugars, and for each sugar, C rather than O sites are always preferred for radicalization, thus suggesting the possibility to activate C-H bonds of biomass sugars. Radical catalysis is further combined with Brønsted acids, and it clearly states that functionalization fundamentally regulates the catalytic effects of biomass sugars. In presence of explicit water molecules, functionalization significantly affects the activation barriers and reaction energies of protonation rather than dehydration steps. Tertiary butyl and phenyl groups with large steric hindrances or hydroxyl and amino groups resulting in high stabilities for protonation products drive the protonation steps to occur facilely at ambient conditions.

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