SYNTHESIS OF CeO_2 NANOPARTICLES BY PRECIPITATION: TEMPERATURE DEPENDENCE OF PARTICLE GROWTH

摘要

Ceria (CeO_2) materials with a cubic fluorite crystal structure (CaF_2) exhibit interesting properties such as chemical reactivity, electrical conductivity, oxygen transport and storing ability. These properties are largely due to the redox chemistry of ceria associated with the ease of Ce~(4+)/Ce~(3+) redox cycles and its high affinity for oxygen. Ceria is often employed as a so-called three way catalyst in SO_x removal technology, NO_x reduction, and as a promoter in the water-gas shift reaction. Ceria nanoparticles display good catalytic activity compared to their bulk counterparts. A uniform distribution of CeO_2 nanoparticles of improved crystallinity is desirable for applications in catalysis. The growth of nanoparticles is preceded by a nucleation process which can occur by solid-state restructuring of a gel or precipitation from a saturated solution. Parameters like temperature, pressure, solution type and aging time determine the particle size. This study investigated the morphology of CeO_2 nanopowders synthesized at two different temperatures.