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

Abstract

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.