Solid state reactions of nanocrystalline Ce0.5Yb0.5O1.75 mixed oxide with high surface area silica in oxidizing and reducing atmosphere

The interaction of nanocrystalline Ce0.5Yb0.5O1.75 mixed oxide with a high surface amorphous silica support in an oxidizing and reducing atmosphere was studied by XRD, HRTEM, SAED, SEM and BET techniques. The Ce0.5Yb0.5O1.75–SiO2 system shows very high structural and size stability in the oxidizing atmosphere up to 1000 °C, but in hydrogen spreading of the oxide onto silica occurs at temperatures above 800 °C. In the oxidizing atmosphere stability of the mixed oxide is limited by extraction of ytterbium from the oxide driven by a tendency to form ytterbium silicates. A new polymorph of Yb silicate, isomorphic with y-Y2Si2O7 (yttrialite), has been identified in the samples containing the mixed Ce–Yb oxide. The absence of y-Yb2Si2O7 silicate in the Yb2O3–SiO2 samples treated in similar conditions indicates that Ce4+ ions are needed to stabilize the structure.

Structure evolution of nano-Ce0.5Yb0.5O1.75–SiO2 in air and in H2. Figure optionsDownload as PowerPoint slideHighlights
► Nano-Ce0.50Yb0.50O1.75 on SiO2 is stable in air up to 1000 °C but spreads in hydrogen at 800 °C.
► Formation of Yb silicates determines the stability of Ce0.50Yb0.50O1.75 at high temperatures.
► New, y-Yb2Si2O7 silicate (yttrialite type) forms in Ce0.5Yb0.5O1.75–SiO2 in H2 at 1100 °C.