Recent Advances in Catalytic Oxidation in Supercritical Water

This article summarizes recent research in homogeneous and heterogeneous catalytic oxidation in supercritical water. We consider both selective partial oxidation for chemical synthesis and complete oxidation for waste destruction. Recent advances in selective catalytic oxidation in supercritical water center around the conversion of p-xylene to terephthalic acid catalyzed homogeneously by MnBr2. Terephthalic acid yields of >90 mol% can be achieved from reactions at 400°C. Using water as the reaction medium provides genuine opportunities for both a more economical and more environmentally benign terephthalic acid production process. Recent advances in complete oxidation via catalysis in supercritical water include the demonstration of heteropolyacids as effective homogeneous oxidation catalysts, and alkali carbonates and carbons as effective heterogeneous catalysts. Additionally, progress has been made in screening transition metal oxide catalysts and determining the reaction-induced chemical and physical changes that take place in the hydrothermal environment. Bulk MnO2 is a good catalyst for complete oxidation because it combines high activity, hydrothermal stability, activity maintenance, and resistance to metal leaching under reaction conditions.