Sustainable Hydrogen Production by Glycerol and Monosaccharides Catalytic Acceptorless Dehydrogenation (AD) in Homogeneous Phase

In the quest for sustainable hydrogen production, the use of biomass-derived feedstock is gaining importance. Acceptorless Dehydrogenation (AD) in the presence of efficient and selective catalysts has been explored worldwide as a suitable method to produce hydrogen from hydrogen-rich simple organic molecules. Among these, glycerol and sugars have the advantage of being cheap, abundant, and obtainable from fatty acid basic hydrolysis (biodiesel industry) and from biomass by biochemical and thermochemical processing, respectively. Although heterogeneous catalysts are more widely used for hydrogen production from biomass-based feedstock, the harsh reaction conditions applied limit applicability due to deactivation of active sites due to coking  of carbonaceous materials. Moreover, heterogeneous catalyst are more difficult to fine-tune than homogeneous counterparts, and the latter also allow for high process selectivities under milder conditions. The present Concept article summarizes the main features of the most active homogeneous catalysts reported for glycerol and monosaccharides AD. In order to directly compare  hydrogen production efficiencies, the choice of literature works was limited to reports where hydrogen was clearly quantified by yields and turnover numbers (TONs). The types of transition metals and ligands is discussed, together with a perspective view on future challenges of homogeneous AD reactions for practical applications.