Structural Reversibility of LaCo1‐xCuxO3 Followed by In Situ X‐ray Diffraction and Absorption Spectroscopy

• Published in: Chemphyschem 2018-08, Vol.19 (15), p.1876-1885
• Main Authors: Pereñíguez, Rosa, Ferri, Davide
• Format: Article
• Language: English
• Subjects: Absorption spectroscopy; Chemical reactions; Copper; in situ XAS; in situ XRD; LaCoO3; Organic chemistry; Oxidation; Oxides; Perovskites; Reduction; Scanning electron microscopy; Spectrum analysis; structure reversibility; X-ray diffraction
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201800069

Combinations of perovskite‐type oxides with transition and precious metals exhibit a remarkable self‐regenerable property that could be exploited for numerous practical applications. The objective of the present work was to study the reversibility of structural changes of perovskite‐type oxides under cyclic reducing/oxidizing atmosphere by taking advantage of the reducibility of LaCoO3. LaCoO3±δ and LaCo0.8Cu0.2O3±δ were prepared by ultrasonic spray combustion and were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), X‐ray absorption spectroscopy (XAS) and temperature‐programmed reduction (TPR). XRD and XAS data confirmed that copper adopted the coordination environment of cobalt at the B‐site of the rhombohedral LaCoO3 under the selected synthesis conditions. The structural evolution under reducing atmosphere was studied by in situ XRD and XANES supporting the assignment of the observed structural changes to the reduction of the perovskite‐type oxide from ABB'O3 (B’=Cu) to B’0/ABO3 and to B’0B0/A2O3. Successive redox cycles allowed the observation of a nearly complete reversibility of the perovskite phase, i. e. copper was able to revert into LaCoO3 upon oxidation. The reversible reduction/segregation of copper and incorporation at the B‐site of the perovskite‐type oxides could be used in chemical processes where the material can be functionalized by segregation of Cu and protected against irreversible structural changes upon re‐oxidation. Reversible structures: The cations (Co3+,Cu3+) inserted on B‐site of the perovskite can be reduced by forming metallic particles on the surface of the resulting La2O3. After an oxidative treatment, the Co and/or Cu particles go back inside the structure lattice, regenerating the perovskite.