PHYSICOCHEMICAL CHARACTERIZATION OF CERIA AS A FINAL DECOMPOSITION PRODUCT OF AMMONIUM CERIUM(III) OXALATE HYDRATE

High surface area and porous ceria was produced as a final decompositi on product of ammonium cerium(III) oxalate hexahydrate. Thermal proces ses involved in the decomposition of (NH4)(2)Ce-2(C2O4)(4).6H(2)O on h eating up to 500 degrees C in air were monitored by differential therm al analysis (DTA) and thermogravimetric analysis (TG) at various heati ng rates. Intermediates and final solid products were characterized by X-ray diffraction (XRD) and IR spectroscopy. The results indicated th at the decomposition takes place via five weight loss processes; three endothermic with peaks at 110, 170 and 290 degrees C and two exotherm ic at 320 and 335 degrees C. The formation of anhydrous ammonium salt occurs at 170 degrees C, and this decomposes at 290 degrees C giving r ise to the unstable intermediate hydrogen eerie oxalate, the latter de composing immediately to Ce-2(CO3)(3) and Ce2O(CO3)(2) at 320 degrees C. The unstable carbonates undergo an oxidative decomposition to give the final product, CeO2, at 335 degrees C. Surface texture analysis an d scanning electron microscopy showed that CeO2, when produced at 300 and 400 degrees C, had a surface area of 130 m(2) g(-1) and 120 m(2) g (-1), respectively and was a crystalline porous material.