Applying ElectromagneticWet Quenching to RealizeCrystal-Phase Engineering of Metal Oxides for Enhanced Catalytic Oxidation

The development of high-performance catalysts to remove volatile organic compounds (VOCs) is of great interest. Catalytic oxidation strongly depends on increasing oxygen vacancy (V_O) formation and the V_O capacity to activate O₂. Here, we report a new method, electromagnetic wet quenching (EWQ), as an alternative to the traditional hydrothermal method for crystal-phase engineering. The EWQ strategy relies on the sharp temperature difference between the magnetocaloric reactor surface and solution bulk to realize repeated spontaneous quenching, which we validate through conducting experiments and theoretical calculations. A wide range of nanocrystalline metal oxides, such as α-MnO₂, β-MnO₂, and CeO₂, can be synthesized quickly and easily using the EWQ method. The one with the lowest apparent activation energy (73.2 kJ/mol) for the catalytic oxidation of toluene is EWQ-CeO₂ produced by using the EWQ method. We can directly examine the crystal-phase effect by combining EWQ and hydrothermal techniques with the same synthetic formula, which allows for some control over the crystallographic phase without altering the composition. The formation of a heterostructured phase is found to enhance V_O generation and activity, which is responsible for the high performance of EWQ-CeO₂ in the low-temperature catalytic oxidation of VOCs.