engleski

Thermal analysis of hydrothermally-derived, manganese-doped ceria

Ceria (CeO2) is utilized as a catalyst in various environmental applications. Its catalytic properties are mostly attributed to high oxygen storage capacity. Ceria has flourite structure in which oxygen vacancies occur due to occurrence of cerium in two stable oxidation states, Ce4+ and Ce3+. The easiness of shift between Ce3+ and Ce4+ enables the creation of oxygen vacancies, high oxygen mobility and oxygen storage capacity within the lattice. [1] Doping of cerium oxide improves its catalytic properties in relation to pure cerium oxide. Manganese oxides are known for being capable of storing oxygen and forming many oxides with various oxidation states. MnOx compounds are highly catalytically active and it is believed that incorporation of Mn atoms in ceria crystal lattice will also improve its catalytic properties. Cerium oxide both doped and pure can be prepared in many ways. The advantages of hydrothermal process are one-pot synthesis, cost-effectiveness and eco-friendliness since it allows obtaining of nanoparticles at low temperatures in just one step. [2] Therefore, nano-ceria doped with manganese in various amounts was prepared via hydrothermal synthesis and the obtained ceria samples were thermally treated at 500°C for 2h. Both, as-prepared and thermally treated samples were investigated using X-ray diffraction (XRD). It was determined that in the diffraction patterns of as-prepared doped samples, beside ceria, birnessite (Na0.55Mn2O4×1.5H2O) lines appear. In the course of thermal treatment birnessite transforms to α- MnO2. Ceria lattice constant and crystallite size, as well as birnessite share, were obtained through whole powder pattern decomposition. It was established that the share of Mn entering ceria lattice, or forming birnessite varies with nominal composition. However, introduction of Mn in ceria is evident from the slight decrease of ceria lattice constant while crystallite size does not change significantly. Decrease of ceria lattice constant with the increase of Mn share could also be observed in thermally treated samples. Also, although thermal treatments yield with coarsening of crystallites, the decrease of ceria crystallite size with increase of manganese share is evident. Thermally induced changes were monitored via differential thermal analysis and thermo-gravimetric analysis (DTA/TGA) giving insight into birnessite dehydration. Calculation of birnessite share via TGA yield with similar values as obtained using XRD. The compliance of samples composition with nominal was confirmed using energy dispersive X-ray spectroscopy (EDS) while the scanning electron microscope (SEM) analysis revealed birnessite layered formations surrounded with ceria nanoparticles.

doped ceria ; hydrothermal synthesis ; manganese

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