The reactivity of CeO2 towards MoO3 in air atmosphere – reinvestigation

Abstract

AbstractIt is known that both the type and possibilities of application of cerium molybdates(VI) largely depend on the methods of their synthesis. Despite this, information on the type of molybdates(VI) formed as a result of a waste-free and environmentally friendly reaction occurring in the solid state between CeO2 and MoO3 in the air atmosphere, are divergent. The conducted research indicates that CeO2 and MoO3 react in air and in the temperature range of 500–650 °C to form two compounds, i.e. Ce5Mo8O32 and/or Ce2Mo4O15. Only the Ce5Mo8O32 compound, for the first time, was obtained as a pure phase. The synthesis of Ce5Mo8O32 takes place through an intermediate stage. In this stage, with the evolution of oxygen, the compound Ce2Mo4O15 is formed, which then reacts with excess CeO2 to Ce5Mo8O32. The obtained compound was characterized by XRD, DTA–TG, FTIR and UV–Vis/DRS methods. Ce5Mo8O32 has a green-olive colour and a density of 4.82 ± 0.05 g cm−3. It was found that this compound melts incongruently at the temperature of 960 ± 5 °C with the separation of solid CeO2. The value of the energy gap Eg ~ 2.59 eV allows the Ce5Mo8O32 compound to be classified as a semiconductor. The previously unknown properties of the compound with mixed cerium valence (Ce 4 3+ Ce4+Mo 8 6+ O32), characterized in this work, will constitute the basis for its application research.