Molecular hydrogen (H2) is an indispensable reactant in modern chemistry, used in many industrial processes for both commodity and fine chemicals synthesis. Unfortunately, the most widely spread production method of hydrogen (reforming of methane) is unsustainable due to the generation of carbon dioxide and moreover on a longer term not guaranteed because of the depletion of fossil feedstocks. Fortunately, many alternative solutions for (large scale) sustainable hydrogen production are technically far advanced, such as electrolysis. However, due to the issues related to the safe handling and storage of hydrogen, its use immediately after production (in situ generation and consumption) is the ideal approach for reactions using hydrogen as a reductant in the chemical industry. This ideally requires production and consumption of hydrogen in the same reaction vessel based on donor molecules which do not produce organic by-products. Thermochemical in situ water splitting combined with subsequent reduction reactions consuming hydrogen is a very attractive approach due to the practically unlimited availability of water and its very benign profile as a solvent (low cost, no environmental impact, non-toxic, non-flammable). However current (catalytic) methods for thermochemical water splitting are performed in gas phase and require very high temperatures (above 600 °C) and therefore are both extremely energy-demanding and incompatible with most organic molecules (these are not stable at these temperatures). The major objective of this project is therefore to develop thermochemical water splitting combined with immediate consumption of the generated hydrogen in a subsequent reduction (hydrogenation/hydrogenolysis) reaction at lower temperatures (200-300 °C) in liquid high temperature and pressure water (HTPW). At these temperatures, the properties of water remarkably change, providing much better solubility of organic substrates – often an issue for application of water in organic synthesis. Development of new synthetic methods for sustainable reduction reactions (nitro group reduction, hydrodeamination, hydrodehydroxylation) of both petrochemical and renewable feedstocks in HTPW are scheduled in which hydrogen gas will be generated in situ and consumed in the same reaction vessel. Several thermochemical systems for hydrogen gas generation will be evaluated, making use of both homogeneous and heterogeneous catalysts to bring down the required temperatures. The combined hydrogen production/reduction process will be optimized by variation of numerous parameters (temperature, pressure, concentration, catalysts and their loading, catalytic additives for the H2 generation). Due to the multiple (not independent) parameters which need to be varied, a "Design of Experiments (DoE)" approach will be used rather than the "vary one parameter at a time". Furthermore, design and optimization of all above-mentioned synthesis routes require a detailed insight into the reaction mechanisms on a molecular level. Therefore the mechanism of both the non-metal catalyzed reduction reactions and metal catalyzed hydrogen gas production will be studied with various experimental (spectroscopic) and computational techniques. In addition, for reactions relying on heterogeneous catalysis, thorough characterization of the catalyst's structural features by various techniques (e.g. XRD, UV-DR, Raman spectroscopy) will be undertaken.