Structure, morphology and surface properties of nanostructured ZrO2 particles

Abstract

Nanocrystalline zirconium dioxide particles have been produced by means of thermal decomposition of a liquid metal organic precursor in a flow reactor system. X-Ray diffraction patterns show that the powder consists of a mixture of the monoclinic and tetragonal phase and that the phase fractions depend on the experimental conditions during the preparation as well as on the subsequent thermal treatment of the sample. The mean particle diameter of the synthesized powders is ca. 40-50 A ˚as estimated from the line width of Bragg reflections and from transmission electron micrographs. The crystallites are non-porous and exhibit a rough surface incorporating a high concentration of low-coordinated surface sites. In agreement with the small particle size, the powder has a high specific surface area (>200 m2 g−1), which surmounts that of commercially available materials by a factor >3. The structure and morphology of the particles is essentially preserved during extensive thermal treatment up to 500 °C. Hydroxyl groups as IR active surface probes clearly indicate that the phase fractions on the surface and in the bulk strongly differ from each other.Low-coordinated OH groups on monoclinic surface domains give rise to H/D exchange reactions with D 2 already at room temperature. They are evidenced and monitored with time by FTIR spectroscopy.

CO2 utilization for the formation of styrene from ethylbenzene over zirconia-supported iron oxide catalysts

“…The preceding bands in each part are assigned to low-coordinated Zr 4 (or Ce 4 )-OH, whereas the subsequent bands are assigned to low-coordinated O-H derived from H 2 O. 12 Lowcoordinated Zr 4 (or Ce 4 )-OH on Ce-ZrO 2 is dominant even after desorption of CO 2 at 300°C. It has been reported that the formation of the stronger Lewis acid (Zr 4 or Ce 4 ) and base (surface O 2À ) sites is favorable for CO 2 activation.…”

“…It has been reported that the formation of the stronger Lewis acid (Zr 4 or Ce 4 ) and base (surface O 2À ) sites is favorable for CO 2 activation. 12,13 The more pronounced intensity attributed to the formation of planar polydentate carbonates (1466 and 1406 cm À1 ) on Ce-ZrO 2 indicates the closeness of cations, which is characteristic of the tetragonal structure of ZrO 2 . 14 For zirconia the bands assigned to bidentate carbonates (1550 and 1331 cm À1 ) and hydrogen carbonates (1630, 1427, and 1219 cm À1 ) disappear after evacuation at 300°C, whereas the bands due to hydrogen carbonates (1653, 1431, and 1200 cm À1 ) appear on supported Fe 3 O 4 catalyst after evacuation at 300°C.…”

Crystallite Size Effect on the Tetragonal-Monoclinic Transition of Undoped Nanocrystalline Zirconia Studied by XRD and Raman Spectrometry

“…Let us compare the in#uence of thermal treatment on phase fractions of nanocrystalline zirconia prepared by di!erent routes. A recent study carried out by Benfer et al (33) focused on zirconia prepared by (i) CVD from organic precursors and (ii) #ame hydrolysis from ZrCl (Degussa). Our zirconia were prepared by pyrolysis of nitrates at 6003C (I-6.9) and 9003C (II-13.2).…”

Imaging of low temperature induced SMSI on Pd/TiO2 catalysts

“…Monocrystalline titania anatase (93 m 2 /g) was prepared by chemical vapour deposition method [27] and wet impregnated with Pd(NO 3 ) 2 AE 2H 2 O (Merck) to obtain a metal loading of 2. TiO 2 particles were produced by means of thermal decomposition of titanium isopropoxide vapour in a flow reactor.…”