CHAPTER 3: Catalytic Conversion of Fossil and Renewable Fuel Resources: Approaches Using Sub and Supercritical Water as a Reaction Medium

Access to energy is one of the main challenges society will face in the decades to come. Liquid fuels are expected to remain one of the main sources of energy, despite the depletion of conventional fossil fuel reserves. The development of cleaner technologies to transform unconventional energy resources such as heavy oil, biomass and organic residues into fuels is crucial to meeting the world's future energy demand. Water in hydrothermal conditions near or above the critical point can provide an efficient route to obtain fuels from unconventional sources in a clean and efficient way. For instance, due to its particular physicochemical properties, near-critical water and supercritical water are considered excellent solvents for catalytic organic chemical reactions. In hydrothermal processes, the addition of a catalyst has the purpose of increasing rates of reaction and product yields, suppressing the formation of solids, reducing re-polymerization of intermediate species and promoting cracking reactions. Successful implementation of catalytic processes in hydrothermal conditions requires the development of highly active catalysts that are stable under these conditions without deactivation. In this work, a thorough review of the literature on the application of catalytic hydrothermal processes for the conversion and upgrading of fossil and renewable unconventional fuel resources is presented.