**Abstract**

Catalysts are the most effective and economically feasible way to increase yield of the product(s) in various production processes. The catalysts prepared with innovative approaches could have novel catalytic properties such as increased number of active sites, highly selective to the target product, resistance to deactivation, and extended lifetime. The catalysts with these unique properties could provide significant economic benefits for the production of hydrogen which is currently very expensive. Gasification in hydrothermal conditions has considerable advantages over existing high energy-consuming conversion technologies. Hydrothermal conversion processes take place at mild conditions and wet feed materials such as biomass can be used with no need of drying. However, the absence of practical catalysts in hydrothermal conditions is a main challenge that impedes application of these technologies in large scales. This book chapter focused on the metal catalysts which can be used for hydrothermal gasification processes for high-yielding hydrogen gas production from biomass compounds. The effects of different type of carbon supports, incorporation of heteroatom(s) into catalyst support, different shell structure design, etc., were discussed for hydrogen production in hydrothermal gasification processes.

**Keywords:** hydrogen, hydrothermal, gasification, biomass, metal catalysts
