Ce=O Terminated CeO 2

Beneficial effect of cerium excess on in situ grown Sr0.86Ce0.14FeO3-CeO2 thermocatalysts for the degradation of bisphenol A

Ce-doped SrFeO₃ perovskite-type compounds are known as good thermocatalysts for the abatement of wastewater contaminants of emerging concern. In this work, Sr_0.86Ce_0.14FeO₃-CeO₂ perovskite-oxide systems with increasing amounts of cerium excess (0, 5, 10 and 15 mol% Ce), with respect to its maximum solubility in the perovskite, were prepared in one-pot by solution combustion synthesis and the effects of cerium excess on the chemical physical properties and thermocatalytic activity in the bisphenol A degradation were evaluated. The powders were characterized by powder X-ray diffraction combined with Rietveld refinement, X-ray photoelectron spectroscopy, thermal gravimetry, temperature programmed reduction, nitrogen adsorption, scanning electron microscopy and energy dispersive X-ray spectroscopy techniques. Results highlight that the perovskite structural, redox, surface, and morphological properties are affected by the in situ co-growth of the main perovskite phase and ceria and that a larger cerium excess has a beneficial effect on the thermocatalytic performance of the perovskite oxide-ceria biphasic system, although ceria is not active as a thermocatalyst itself. Perovskite properties and performance are enhanced by the tetragonal distortion induced by the introduction of cerium excess in the synthesis. It is supposed that a larger oxygen mobility and an easier reducibility are among the most relevant features that contribute to superior thermocatalytic properties of these perovskite oxide-based systems. These results also suggest new perspectives in the nanocomposite preparation and their catalytic applications.

Kinetics of Strontium Carbonate Formation on a Ce-Doped SrFeO3 Perovskite

Some perovskites exhibit catalytic activity in the abatement of organic pollutants in water. However, their performance decreases over time, possibly due to forms of poisoning, such as carbonate formation. Here, we present the kinetics of carbonate formation on a Ce-doped SrFeO3 perovskite with formula Sr0.85Ce0.15FeO3−δ (SCF), which can act as a thermocatalyst for the degradation of organic pollutants. The carbonate formation was studied in air, in deionized water, and during degradation of bisphenol A. The formation of SrCO3 occurred for perovskites in aqueous environments, i.e., when dispersed in water or used as catalysts in the degradation of bisphenol A, while no SrCO3 was detected for samples stored in air for up to 195 days. SrCO3 formation was detected using both XRD and ATR-FT-IR, and from the XRD, the crystallite size was found to decrease when carbonates formed. The samples containing SrCO3 showed an increasing mass loss at >610 °C with increasing time used as catalysts or dispersed in water, showing that SCF reduces its own efficiency during catalytic use. The kinetics of carbonate formation based on the TGA measurements showed that SrCO3 forms approximately three times faster during the degradation of organic compounds in water compared to SCF dispersed in water. The formation of SrCO3 in SCF is thermally reversible; thus, the catalyst can resume its activity after heat treatment at 900 °C for 1 h.