Photocatalytic H-2 and Added-Value By-Products - The Role of Metal Oxide Systems in Their Synthesis from Oxygenates

The growing demand for hydrogen for industrial use and as a fuel pushes for innovative and sustainable production strategies, which can be applied both in centralized, large-scale plants and in delocalized small units. At present, hydrogen is mainly produced by steam reforming of natural gas or oil. Nevertheless, the shortage of fossil fuel reserves and the increasing concern regarding environmental pollution have stimulated the search for alternative production routes, among which photocatalysis over metal oxide semiconductors represents a strategically attractive solution. Whereas the direct splitting of water is still a challenging issue because of intrinsic process drawbacks, a valuable alternative for a sustainable photocatalytic H-2 production is the use of biomass-derived compounds as raw materials. Upon photoactivation in the presence of an appropriate semiconductor, such feedstocks can undergo oxidation to CO2 with simultaneous H-2 production in the so-called photoreforming process. When the oxidation is selective rather than complete, the process might be of further interest due to the added value of the obtained carbon-containing by-products. This microreview focuses on recent developments in this field, with particular attention to the use of representative biomass-derived oxygenated compounds, such as methanol, ethanol, glycerol, and sugars.