Recent advances in supercritical water gasification of biowaste catalyzed by transition metal-based catalysts for hydrogen production

Supercritical water gasification (SCWG) is a remarkably efficient technology for converting wet biowaste (such as food waste, paper industrial waste, sewage sludge, agricultural waste, and forestry residue) into energy in the form of hydrogen-rich syngas. Catalysts have been widely used for promoting the hydrogen production rate of SCWG at mild reaction temperatures. In this regard, transition metal-based catalysts have attracted extensive attention from researchers due to their excellent performance and recyclability. Herein, the catalytic effects of transition metal-based catalysts on the SCWG of biowaste are reviewed, including the influence of active components, synthetic methods, and support materials. The modification of transition metal-based catalysts (rare earth oxide-promoted catalysts, noble-metal bimetallic catalysts, noble-metal-free bimetallic catalysts, and alkaline-earth metal-promoted catalysts) is also discussed. Finally, technical challenges and future perspectives for the development of transition metal-based catalysts in the SCWG of biowaste are presented. This review paper aims at providing an important reference for the design of transition metal-based catalysts with excellent catalytic performance and physicochemical properties and their applications in the SCWG of biowaste.