INFLUENCE OF LATTICE STRAIN ON THE Ce_(0.5)Zr_(0.5)O_2 AND Al_2O_3 DOPED Ce_(0.5)Zr_(0.5)O_2 CATALYTIC POWDERS

摘要

Ce_(0.5)Zr_(0.5)O_2 has been widely used in three-way catalyst (TWC). However, the thermal resistance is deteriorated at high temperature due to the phase separation of Ce_(0.5)Zr_(0.5)O_2. The phase separation and crystallite growth of Ce_(0.5)Zr_(0.5)O_2 could be inhibited by adding Al ions. In this study, both the Ce_(0.5)Zr_(0.5)O_2 and Al_2O_3 doped Ce_(0.5)Zr_(0.5)O_2 catalytic powders were synthesized via chemical co-precipitation method. The phase separation of Ce_(0.5)Zr_(0.5)O_2 samples was observed as the calcination temperature was raised above 1100 °C. However, the Al_2O_3 doped Ce_(0.5)Zr_(0.5)O_2 samples could maintain single phase till 1200°C. The Williamson-Hall method was employed on the X-ray peak profile of these powders to determine the variation of lattice strain. The phase separation of Ce_(0.5)Zr_(0.5)O_2 samples was observed due to the lattice strain induced by the occurrence of Oxygen vacancies as the calcination temperature was raised to 1100 °C. The Al_2O_3 doped Ce_(0.5)Zr_(0.5)O_2 samples had similar phenomenon but the phase separation temperature was delayed to 1200 °C due to the diffusion barrier effect of Al ions.