Cordierite/CeO2 ceramic nanocomposites from vermiculite with fixed CeO2 nanoparticles, talc and kaolin

Abstract

Ceria-based metal oxides are promising redox materials for photocatalytic decomposition of N2O emissions. The objective of this work was to evaluate the structural properties of cordierite ceramics with anchored CeO2 nanoparticles produced by sintering talc, kaolin and vermiculite with CeO2 nanoparticles precursor. In this contribution, we discuss the effect of the presence of CeO2 nanoparticles on the softening and crystallization temperatures of cordierite, and the influence of the sintering procedure on the microstructure properties of the anchored CeO2 nanocrystals. The materials were characterized by X-ray diffraction analysis, differential thermal analysis and morphology of ceria nanoparticles was visualized in a high-resolution transmission electron microscope (HRTEM). The chemical interactions between CeO2 and the clay minerals were investigated using energy dispersive X-ray spectroscopy in the scanning transmission electron microscope (STEM) and complemented by the Raman measurements. X-ray diffraction revealed that the sintered ceramics contain cordierite-indialite, orthoenstatite and protoenstatite. Differential thermal analysis showed that the addition of 3 mass% of CeO2 decreases the softening and the crystallization temperature of cordierite by approximately 50 degrees C. HRSTEM/EDS observed the Fe concentration of CeO2 nanoparticles, probably due to migration of Fe3+ ions from vermiculite in crystallizing cordierite. The hypothesis of Fe dopant in ceria was proven by local chemical analysis, which was performed with the aid of an EDX line scan in the HRSTEM, by the shift of the Raman CeO2 F-2g mode to lower wavenumbers and by the presence of a Raman band from oxygen vacancies.