Recent advances in heterogeneous catalysis for supercritical water oxidation/gasification processes: Insight into catalyst development

Supercritical water processes include supercritical water (SCW) oxidation (SCWO) and supercritical water gasification (SCWG). These are promising green technologies to address critical solid waste and wastewater management challenges, and in producing clean and renewable energy. Both SCWO and SCWG can use catalysts to improve reaction performance, such as to treat biomass at more moderate temperatures in SCWO processes, and to increase selectivity for production of more desirable gas products in SCWG processes. Heterogeneous catalysis has shown to be advantageous compared to homogenous catalysis for SCW processes. This paper reviews literature on heterogeneous catalysis applied to SCWO and SCWG process from the past decade, by focusing on catalyst preparation, characterization, and mechanisms, primarily for wastewater treatment and biogas production applications. The findings show that metal oxide catalysts such as Ag2O, CeO2, CuO, Fe2O3, MgO can enhance SCWO of biomass. On the other hand, transition metal catalysts (mainly nickel- and ruthenium-based catalysts) have been more often used for SCWG of biomass in SCW, compared to metal oxides, noble metals, zeolites, and carbon-based catalysts. (c) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Automated summary

Supercritical water processes, including SCWO and SCWG, are promising green technologies for solid waste and wastewater management, as well as clean renewable energy production. The use of catalysts can improve reaction performance, such as treating biomass in SCWO processes and increasing selectivity for desirable gas products in SCWG processes. Metal oxide catalysts have been found to enhance SCWO of biomass, while transition metal catalysts are more commonly used for SCWG of biomass in SCW compared to other types of catalysts.