Phase Segregation in Cerium−Lanthanum Solid Solutions

Abstract

Electron energy-loss spectroscopy (EELS) in combination with scanning transmission electron microscopy (STEM) reveals that the La enrichment at the surface of cerium-lanthanum solid solutions is an averaged effect and that segregation occurs in a mixed oxide phase. This separation occurs within a crystalline particle, where the dopant-rich phase is located at the surface of the dopant-deficient phase. The limiting structure appears to be a solid solution with a La fraction of x ) 0.6 in the bulk and x ) 0.75 at the surface. Up to a La fraction of 0.6, this phase will coexist with a lanthanum-type structure in different proportions depending on the dopant amount. STEM-EELS appears to be a powerful technique to clarify the existence of a multiphase system, and it shows that XRF, XPS, and XRD measure averaged results and do not show the phase complexity of the solids.

Highly stable, mesoporous mixed lanthanum–cerium oxides with tailored structure and reducibility

“…Beyond the pure oxides, growing interest is focusing on mixed cerium and other rare earth oxides 4,[13][14][15] . Doped lanthana nanoparticles are of interest as chemically stable photoluminescent materials 16 , and doped ceria shows strongly 30 improved performance as catalyst support and oxygen storage component in applications such as automotive exhaust control 4,[17][18][19] . The latter is due to the fact that-unlike many traditional support materials-cerium oxide plays an important, active role as oxygen storage and oxygen transfer material in redox 35 reactions based on the facile conversion between Ce 4+ and Ce 3+ on the oxide surface.…”

“…Previous studies reported phase separation of mixed La 2 O 3 -CeO 2 at elevated temperature 17,18 , and the solubility limit for La 2 O 3 -CeO 2 solid solutions prepared by 50 various methods is typically reported to be between 40%-70% 14,17,[19][20][21] .…”

Oxidative steam reforming of ethanol over Rh catalyst supported on Ce1−xLaxOy (x = 0.3) solid solution prepared by urea co-precipitation method

“…3. It was observed that the content of La on the surface was a little higher than that in the bulk, which means the surface was slightly enriched with La 3þ [17,25]. With increase in precipitant concentration, the surface enrichment of La was more pronounced.…”

“…Ce 1Àx La x O y solid solutions (CL) can be prepared by citric acid sole gel [23], mechanically mixed high-temperature solid state reaction [24,25], traditional co-precipitation [17], well-controlled NH 4 HCO 3 co-precipitation [26,27] and the urea decomposition by coprecipitation method [22,28]. Among them, the urea coprecipitation method is extensively applied because it is a simple environmental friendly method [29] and good catalytic performance is frequently obtained with ceria-containing mixed oxides [30].…”

The Effect of Precipitants on Ce-La Solid Solution Prepared from Mixed Rare Earth Chloride by a Co-Precipitation Method

“…Ce 1-x La x O y solid solution (CL) can be prepared by many methods, but Ce and La will exhibit phase segregation with La loading and calcination temperature increasing, and the range limits can be affected by the preparation method [32]. It was reported that thermal decomposition of Ce 1-x La x (OH)CO 3 (a precipitates from co-precipitation method) favored the formation of CL and avoided phase segregation [33].…”