Effect of the La(OH)3 preparation method on the surface and rehydroxylation properties of resulting La2O3 nanoparticles

Several lanthanum hydroxides (28–146 m2/g) were prepared by different procedures involving precipitation and hydrothermal methods by conventional heating or with microwaves. The use of ultrasounds during precipitation led to the formation of additional crystalline phases whereas the aging treatment with microwaves decreased the temperature needed to form the lanthanum oxide phase when compared with the samples aged by conventional heating. After calcination, La2O3 samples showed similar BET surface areas (3–5 m2/g) but different particle sizes ranging from 150 to 600 nm depending on the La(OH)3 preparation method, as observed by TEM. La2O3 samples were completely rehydroxylated after 80 h of exposure to atmospheric air at controlled humidity conditions recovering only partially the surface areas of the La(OH)3 precursors (14–18 m2/g). The progress of rehydroxylation with time occurred in several steps at different rates. Rehydroxylation rate mainly depended on the particle size and surface area of the lanthanum oxide sample. Therefore, the method used to prepare the initial lanthanum hydroxide affects the surface and rehydroxylation properties of the subsequent lanthanum oxide sample.