Structural and thermal properties of Co-Cu-Fe hydrotalcite-like compounds |
| |
Authors: | Amadeu H Iglesias Daniel X Gouveia Antonio G Souza Filho Josué Mendes Filho |
| |
Institution: | a LQES-Laboratório de Química do Estado Sólido, Instituto de Química, State University of Campinas (UNICAMP), P.O. Box 6154, zip code 13081-970, Campinas, SP, Brazil b Departamento de Física, Universidade Federal do Ceará, P.O. Box 6030, zip code 60455-900, Fortaleza, CE, Brazil c Centro Federal de Educação Tecnológica-CEFET, zip code 60040-531, Fortaleza,CE, Brazil |
| |
Abstract: | The structural properties and thermal decomposition processes of Co-Cu-Fe ternary hydrotalcites (HT) have been studied through X-ray diffraction, thermogravimetric measurements, Fourier-transform infrared and Mössbauer spectroscopies. Due to the strong Jahn-Teller effect, the Cu-Fe layered system is stabilized only in the presence of Co2+. At low Co2+ contents, additional phases are segregated in the solids. X-ray patterns show the presence of Cu(OH)2 and CuO. The decomposition process was investigated by in situ X-ray, in situ Mössbauer and FTIR experiments. By increasing the temperature from 25 °C up to 180 °C we observed that the structural disorder increases. This effect has been likely attributed to the Co2+→Co3+ oxidation since thermal decomposition was carried out under static air atmosphere. Part of the Co3+ cations could migrate to the interlayer region, thus forming a metastable compound that still has a layered structure. Collapse of the layered structure was observed at about 200 °C. By further increasing the temperature the system becomes more crystalline and the formation of Co3O4 is observed in the X-ray patterns. In Cu-rich HT, some of the carbonate anions are released at temperatures higher than 550 °C and this phenomenon is attributed to the formation of a carbonate-rich phase. The specific surface area data present its highest values in the temperature range where the collapse of the layered structure takes place. |
| |
Keywords: | Layered double hydroxides Hydrotalcite-like compounds Anionic clays Thermal decomposition Mixed oxides 57Fe Mö ssbauer spectroscopy Decomposition mechanism Copper |
本文献已被 ScienceDirect 等数据库收录! |
|