Interaction of Ce_1−xEr_xO_2−y nanoparticles with Al₂O₃

The interaction of nanocrystalline Ce_0.5Er_0.5O_1.75 mixed oxide with an amorphous Al₂O₃ in oxidizing and reducing atmosphere up to 1100 °C was studied by XRD, TEM, SEM-EDS and BET. Uniform, chemically homogeneous Ce_0.5Er_0.5O_1.75 nanoparticles (2 nm in size) were prepared by microemulsion method and deposited on a high surface γ-alumina support. The nanoparticles were structurally and chemically stable in the oxidizing atmosphere up to 1100 °C, exhibiting only an increase of the mean crystallite size to 9 nm after 3 h treatment. Prolonged heating (24 h) at 1100 °C caused partial decomposition of the mixed oxide and reaction of the extracted erbium with the support with formation of hexagonal (P6₃/mmc) ErAlO₃ aluminate. The same hexagonal ErAlO₃ occurred also in Er/Al₂O₃ sample prepared by impregnation of Al₂O₃ support with an aqueous solution of Er nitrate and subjected to heating in air or hydrogen at 1100 °C. In the reducing atmosphere the Ce_0.5Er_0.5O_1.75 reacted with Al₂O₃ already at 800 °C, to form an amorphous surface phase. At 900 °C monoclinic (P2₁/c) (Er,Ce)₄Al₂O₉ mixed aluminate was formed with the unit cell volume 4.5% bigger than that of pure Er₄Al₂O₉ phase. After 3 h treatment at 1000 °C more than half of the (Er,Ce)₄Al₂O₉ aluminate decomposed into two nanocrystalline mixed monoaluminates: tetragonal (I4/mcm) (Ce,Er)AlO₃ and hexagonal (P6₃/mmc) (Er,Ce)AlO₃. Nanocrystalline mixed aluminate particles with Er³⁺ ions placed in well-defined lattice sites and supported at the surface of Al₂O₃ support, may be interesting as highly efficient active components of optical waveguides amplifiers. - Graphical abstract: Structure evolution of Ce_0.5Er_0.5O_1.75 on Al₂O₃ in air and in H₂. - Highlights: • Homogeneous 3 nm Ce_0.5Er_0.5O_1.75 particles were prepared and uniformly dispersed on Al₂O₃. • Er diffusion to Al₂O₃ determines the stability of the mixed oxide in air to ∼1100 °C. • Reaction of Ce_0.5Er_0.5O_1.75 with Al₂O₃ occurs in hydrogen at 800 °C. • Nanocrystalline (Ce,Er)₄Al₂O₉ aluminate forms in H₂ at 900 °C