THERMAL-DECOMPOSITION OF PURE AND RHODIUM IMPREGNATED CERIUM(III) CARBONATE HYDRATE IN DIFFERENT ATMOSPHERES

The thermal decomposition of pure and rhodium impregnated cerium(III) carbonate hydrate in oxidising, reducing and inert atmospheres has bee n studied using combined thermogravimetry/mass spectrometry (TG/MS) an d X-ray photoelectron spectroscopy (XPS). In oxygen, the decomposition of the pure carbonate proceeds in two steps, yielding H2O, CO2, and c erium(IV) oxide. In inert or reducing atmospheres, the second decompos ition step is shifted towards higher temperatures and is divided into two parts. In the second part, CO2 evolved is partly reduced by Ce(III ) to CO and to elemental carbon, and non-stoichiometric CeO2-x, is for med as the solid product. In the presence of rhodium as a reduction ca talyst, decomposition in helium yields hydrogen and less carbon monoxi de than that of the pure carbonate, due to the water-gas shift activit y of the solid. In hydrogen, quantitative reduction of the carbon diox ide evolved to methane and water is observed when rhodium is present.