Thermally induced changes in the oxidation state of cerium(IV)

Abstract

Cesium hexachlorocerateflV), CszCeCI 6 (I) and sodium pentakis(carbonato)cerate(IV), Na6Ce(COa)5.12H20 (II) have been investigated in air by simultaneous TG/DTA, FTIR and XRD in order to follow the oxidation state of cerium during their thermal treatment. The thermal decomposition of the hexachloro compound (I) is accompanied by a double change in the oxidation state of cerium. First, in an inner reduction-oxidation reaction, chlorine is evolved and a Cs2CeCI 5 phase is obtained. The immediately starting oxidation of this Ce(III) species caused various phase transitions in the CeCI3--CsC1 system formed. The presence of Cs3CeCI~ above 400~ can also be assumed and finally this phase also oxidizes into CeO 2 with the formation of CsCI as by-product. In the case of the pentacarbonato complex (II), no Ce(III) species were detected. The final products of its decomposition were CeO2 and NazCO 3.