Improving the Redox Response Stability of Ceria-Zirconia Nanocatalysts under Harsh Temperature Conditions

Abstract

By depositing ceria on the surface of yttrium-stabilized zirconia (YSZ) nanocrystals and further activation under high-temperature reducing conditions, a 13% mol. CeO2/YSZ catalyst structured as subnanometer thick, pyrochlore-type, ceria-zirconia islands has been prepared. This nanostructured catalyst depicts not only high oxygen storage capacity (OSC) values but, more importantly, an outstandingly stable redox response upon oxidation and reduction treatments at very high temperatures, above 1000 °C. This behavior largely improves that observed on conventional ceria-zirconia solid solutions, not only of the same composition but also of those with much higher molar cerium contents. Advanced scanning transmission electron microscopy (STEM-XEDS) studies have revealed as key not only to detect the actual state of the lanthanide in this novel nanocatalyst but also to rationalize its unusual resistance to redox deactivation at very high temperatures. In particular, high-resolution X-ray dispersive energy studies have revealed the presence of unique bilayer ceria islands on top of the surface of YSZ nanocrystals, which remain at surface positions upon oxidation and reduction treatments up to 1000 °C. Diffusion of ceria into the bulk of these crystallites upon oxidation at 1100 °C irreversibly deteriorates both the reducibility and OSC of this nanostructured catalyst.

Boosting the performance and durability of Ni/YSZ cathode for hydrogen production at high current densities via decoration with nano-sized electrocatalysts

“…From the STEM images and EDS maps it can be seen that the Ce-Gd regions on the YSZ surface are present as relatively small particles. The formation of a similar thin Ce-rich particles on the YSZ surface has been reported, when samples were prepared by infiltration of Ce-nitrate solutions and calcination at high temperatures 53,54 .…”

“…The CeO2 -Ni model system has recently been studied for steam reduction reaction [34][35][36] , showing that the CeO2 -Ni interfaces can be crucial points for the steam reduction reaction. A thin Ce-containing layer on the YSZ support, presented in Figure 13a (III), has also been reported as a very efficient three-waycatalyst for the steam reduction reaction, especially due to high oxygen storage capacity and outstanding stable redox response upon oxidation and reduction treatments 53,54 . Based on these findings it cannot be ruled out that the steam electrolysis could occur on the Ce-containing particles on the Ni grains as well as on the Cecontaining particles on the YSZ grains.…”

“…The Cecontaining particles on the YSZ support can form a secondary phase, although no identification of it was found in the here presented study (Figure 13b (III)). For a similar system, after exposure to temperatures higher than 1100 °C a pyrochlore phase was formed, which drastically reduced the activity of the catalyst 54 .…”

Tuning the Integration Rate of Ce(Ln)O2 Nanoclusters into Nanoparticulated ZrO2 Supports: When the Cation Size Matters

“…In the latter case, the authors noticed that an inversion of the intensity of the two reduction peaks took place for CeO 2 crystallites, having sizes of around 5 nm and below. Finally, it should be also highlighted that this TPR diagram obtained on the fresh ZrO 2 -CeO 2 sample closely resembles those earlier reported by our research group for ZrO 2 -and YSZ-supported CeO 2 catalyst formulations, containing similar lanthanoid oxide nominal loadings (i.e., 15 and 13 mol.%, respectively), and prepared by the incipient wetness impregnation method [38,39]. In any case, all these three TPR profiles clearly evidence the effectiveness of the proposed synthetic approach, consisting of depositing CeO 2 in the form of a surface phase, either by incipient wetness impregnation or by the controlled chemical precipitation method herein described, to improve the redox response of the resulting ZrO 2 -CeO 2 systems when compared with a commercial fresh bulk mixed oxide sample with similar Ce to Zr molar ratio (i.e., Ce 0.15 Zr 0.85 O 2 ) and reported elsewhere [38,39].…”

Advances in Functional Metal‐Organic Frameworks Based On‐Demand Drug Delivery Systems for Tumor Therapeutics

“…In MOF systems, ligand design and surface modification are the main key uses for disulfide bonds. [ 127,128 ]…”