STRUCTURAL CHARACTERIZATION AND HYDROGEN ABSORPTION KINETICS OF CexZr1-xO2 SOLID SOLUTIONS PRODUCED BY MECHANICAL MILLING

D. DOMANSKI; M. L. RODRIGUEZ; J. ANDRADE GAMBOA; F. C. GENNARI

Lahaina, Maui, Hawaii

Simposio; MH2006-International Symposium on Metal-Hydrogen Systems; 2006

International Symposium on Metal-Hydrogen Systems

Ceria based solid solutions (CexZr1-xO2, CZ) have been widely used as catalysts in different industrial processes. In these materials some key properties, such as redox behavior, thermal stability and reactivity with hydrogen are associated with the material characteristics (phases and its structure, particle size, surface area) and are dependent of the synthesis method selected. In this work the mechanical milling process has been used successfully for the production of two different CexZr1-xO2 solid solutions (x=0.8 and 0.5, CZ80 and CZ50, respectively) at room temperature and air atmosphere. The evolution of Zr incorporation into CeO2 structure during milling and crystallite size reduction to the nanometric range were determined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Hydrogen absorption kinetics of Pd supported on CZ80 and bare CZ80 were determined using volumetric equipment. For Pd/CZ80 both total hydrogen uptake and absorption rate were dependent of the temperature in the range of 25 to 80 ºC. No hydrogen reduction occurs up to this temperature for CZ80. At higher temperatures (250-400 ºC), hydrogen reduction of CZ80 starts and the kinetic can be fitted with a zero order model. In this case the apparent activation energy is 17 kJ.mol-1, suggesting a reaction mechanism controlled by a non-activated process.