Surface reactivity and bulk properties of ZrO2. Part 2.—Importance of homogeneity in the stabilisation of high surface area CeO2–ZrO2aerogels

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Abstract
CeO2–ZrO2 aerogels (prepared by supercritical drying of the precursor hydrogels produced by either co-precipitation or deposition-precipitation) have been characterised in order to elucidate the effect of the structural homogeneity on the stability of their total surface areas at high temperatures. Co-precipitated aerogels (CPA) had larger and more crystalline particles but showed much higher surface areas than deposited-precipitated aerogels (DPA) after calcination at high temperatures (i.e. 1223 K). The difference originates, it is believed, from their surface structural homogeneity. Differential thermal analysis (DTA) and X-ray diffraction (XRD) revealed that the CPA aerogels had a homogeneous single-phase structure even after calcination at 1223 K, while transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and IR spectrascopy showed that the CPA samples were highly dispersed with homogeneous surfaces in the composition range studied. However, the DPA sample did not have the same homogeneity and appeared to form larger aggregates via inter-particulate contacts due to the high levels of cerium carbonates on their surfaces, which led to the presence of the monoclinic phase and a loss of surface area when the sample was calcined at high temperatures.
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