Synthesis and characterization of Nd³⁺-doped Ce_0.6Zr_0.4O₂ and its doping significance on oxygen storage capacity

Cerium and cerium-based oxides are found to be an important element in three-way catalytic converter (TWC). The effective utilization of TWC is found to be reduced due to thermal loading which results in structural deformation of ceria. Doping Zr⁴⁺ into the rare earth element can increase the oxygen storage capacity and thermal stability. Hence, an attempt was made to study the oxygen storage capacity and thermal stability of ceria by doping Zr⁴⁺ and Nd³⁺. Cerium-based nanocrystallite in the composition of Ce_0.6Zr_0.4−xNd_1.3xO₂ (0 ≤ x ≤ 0.4) was prepared by sol–gel synthesize technique with citric acid as a gel-forming agent. X-ray diffraction (XRD) result shows that doping Nd³⁺ into ceria lattice forms homogenous solid solution of cubic fluorite structure up to 25 % of substitute only. Doping higher amount of Nd³⁺ into ceria lattice leads to the formation of Nd₂O₃. Raman spectrum study confirms that oxygen storage capacity band is present in Ce_0.6Zr_0.4O₂ and Ce_0.6Zr_0.3Nd_0.13O₂. The oxygen storage capacity was calculated through weight loss of the sample during the second heating cycle with cyclic heating from 30 to 800 °C in thermogravimetric analysis (TGA). The TGA study reveals that the oxygen storage capacity of Ce_0.6Zr_0.4O₂ decreases after the substitution of Nd³⁺, which is due to the larger ionic radius of Nd³⁺ compared with that of Zr⁴⁺ and CeO₂.