Key insights on the structural characterization of textured Er2O3–ZrO2 nano-oxides prepared by a surfactant-free solvothermal route

Abstract

Keywords: structural resolution / Er 2 O 3 -ZrO 2 / HRTEM / fluorite / solvothermal route Zirconia-mixed oxides can exhibit cubic fluorite and pyrochlore structure. Their discrimination is not easy in nanooxides with a crystal size close to that of a few unit cells. In this work, High Resolution Transmission Electron Microscopy (HRTEM) has been employed to provide key insights on the structural characterization of a nanometric and porous mixed Er 2 O 3 -ZrO 2 oxide. The material was prepared by a simple template-free solvothermal route that provided nanocrystalline powders at low temperature (170 ºC) with spherical morphology, and high surface area (280 m 2 /g). The porosity was mainly originated from the assembling of organic complexing agents used in the synthesis to limit the crystal growth and to control hydrolysis and condensation reaction rates. The samples were characterized by thermal analysis, X-ray Diffraction, Scanning Electron Microscopy and N 2 adsorption measurements.A detailed study by HRTEM was conducted on microtomed samples. It was observed that the material was made of nanocrystals packed into spherical agglomerates. HRTEM simulations indicated that it is not possible to identify the pyrochlore phase in nanoparticles with diameter below 2 nm. In our samples, the analysis of the HRTEM lattice images by means of Fast Fourier Transform (FFT) techniques revealed well defined spots that can be assigned to different planes of a cubic fluorite-type phase, even in the raw material. Raman spectroscopy was also a powerful technique to elucidate the crystalline phase of the materials with the smallest nanoparticles. HREM and Raman results evidenced that the material is constituted, irrespective of the temperature of the final calcination step, by an ensemble of randomly oriented nanocrystals with fluorite structure. This study opens new perspectives for the design of synthetic approaches to prepare nanooxides (fluorites and pyrochlores) and the analysis of their crystalline structure.____________ [a]

One step microwave-assisted synthesis of nanocrystalline WOx–ZrO2 acid catalysts

“…The reason for this trend lies in the presence of anion vacancies in the metastable tetragonal polymorph originating from the introduction of trivalent or divalent ions. 69 As a consequence, the more ionic character of the tetragonal polymorph induces higher Lewis and Brønsted acidity 63 (see Figure S8 and Table S3) than in the more covalent monoclinic structure. Thus the more acid species stabilized over the tetragonal zirconia could explain the higher activity in the hydration of alkynes.…”

Design of new nanomaterials for their use in catalysis and photochemistry

“…These results become significant when comparing these values with the best results reported in the literature for the same kind of materials. 13,14,39 Additionally, in our work, the amount of sulfide is very low and no additional reducing agents are required, as usually happens with ZnS photocatalysis. 40 Regarding the catalytic activity of the samples synthetized by the solvothermal method and the one prepared by impregnation, we can conclude that the first one is much more active.…”

“…Since the first work of Hino and Arata 11,12 demonstrating the use of tungsten deposited on zirconia as a solid acid for isomerization of light alkanes, several reactions such as oxidative desulfurization, 13 alkylation of phenols, 14 o-xylene isomerization, 15 production of aromatics from alkylfurans, 16 2-butanol dehydration, 17 among others, have been catalyzed by these materials.…”

“…The doped NaYF 4 NPs (Er:Yb 2:20 and Tm:Yb 2:20) were synthetized through thermal decomposition as previously reported by G. S. Yi et.al 14 . Thus, 10 mmol of of NaCF 3 COO and 5 mmol of RE(CH 3 COO) 3 were mixed together with 50 mL of oleylamine and was added to a three-necked flask.…”

“…Pero otras fases metaestables, como la cúbica o tetragonal, pueden ser estabilizadas a temperatura ambiente a través de diversos métodos de síntesis o dopando la matriz con iones divalentes o trivalentes. [12][13][14][15][16] Dichas fases presentan diferente acidez y basicidad en función de su estructura cristalina, lo que les confiere diferente actividad y selectividad en diversas reacciones catalíticas. [17][18][19][20][21] Las propiedades ácidas del ZrO 2 se pueden incrementar con la introducción de molibdeno, tunsgeno o iones sulfato.…”