CeO₂ Structure Adjustment by H₂O via the Microwave-Ultrasonic Method and Its Application in Imine Catalysis

CeO₂ with fusiform structures were prepared by the combined microwave-ultrasonic method, and their morphologies and surface structure were changed by simply adding different amounts of H₂O (1-5 ml) to the precursor system. The addition of H₂O changed the PVP micelle structure and the surface state, resulting in CeO₂ with a different specific surface area (64-111 m² g^-1) and Ce³⁺ defects (16.5%-28.1%). The sample with 2 ml H₂O exhibited a high surface area (111.3 m²∙g^-1) and relatively more surface defects (Ce³⁺%: 28.1%), resulting in excellent catalytic activity (4.34 mmol g^-1 h^-1).