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We investigated the formation of extended defects in CaFeO2.5, predominantly appearing as antiphase boundaries (APBs), as a function of the synthesis method and temperature. While CaFeO2.5 is known to adopt an ordered oxygen defect structure showing long range order of the (FeO 4)? chains in its bulk form, interestingly, we demonstrated that the length of these (FeO4)? chains can be considerably scaled down to few nanometers by adopting a modified sol-gel method (low temperature synthesis) while the grain size of the resulting nano-phase CaFeO2.5 is around 50 nm. We discuss the synthesis dependent modulation of the length of APBs, characterized by X-ray diffraction and high resolution TEM, to be at the origin of an amplified switching dynamics of the (FeO4)? chains. This can accordingly explain the reduction of the onset temperature for oxygen diffusion to set in from 450 �C for bulk-CaFeO2.5 to 320 �C for nano-CaFeO2.5, as determined by 18O/16O oxygen isotope exchange reactions. � 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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Journal of physics / D 48(50), 504004 (2015). doi:10.1088/0022-3727/48/50/504004, Published by IOP Publ., Bristol

LaAlO3 perovskites, as such and with 25% molar Al substitution by Cu, Co, or Ga, have been prepared by sol-gel methods and tested as heterogeneous catalysts in the gas-phase conversion of ethanol. LaAlO3 presented a significant acidic character, with high formation of ethylene by ethanol dehydration. B-site substitutions increased the basicity of the catalysts, favoring the dehydrogenation of ethanol to acetaldehyde. The most reducible Cu- and Co-substituted materials, characterized by easier formation of surface oxygen vacancies, promoted the self-condensation of acetaldehyde by the Tishchenko mechanism, with formation of acetone and odd-carbon number products. Aldol coupling of acetaldehyde, favored on pure and Ga-substituted LaAlO3, led to the formation of butadiene and hexadiene. The role of Ga insertion, favoring both dehydrogenation of ethylene and dehydration of higher alcohols, corresponds to an amphoteric character. The formation of olefins and diolefins on all catalysts suggests that LaAl-based materials present the most acidic character among La-perovskites.