Modification of cerium oxide with different dopants and synthesis methods

Abstract

Cerium oxide has many applications as a reducible oxide. In this paper, different dopants (Sm, Fe, Pt, and Rh) and synthetic methods were used to modify ceria to obtain metal-doped ceria with high specific surface area and high homogeneity. For different synthesis methods, different parameters that may have affect on the specific surface area were also investigated. The synthesized oxides were characterized employing N2-physisorption, XRD, etc. to compare the surface area, crystal structure, and purity. The results showed that different synthesis methods have the greatest influence on the specific surface area, and the co-precipitation method is better than the citric acid method or the modified Pechini method in synthesizing oxides with high specific surface area. In the co-precipitation method, the choice of precipitant also played a role. Among the precipitants tested in this project (ammonia, urea and sodium hydroxide), sodium hydroxide performs best in getting high surface area. Citric acid and Modified Pechini method performed better in obtaining more homogeneous samples. Two typical doped ceria synthesised by sodium hydroxide method were selected as carriers (Ce0.8Sm0.2O1.9, Ce0.8Fe0.2O1.9), and the catalysts were prepared by supporting metal Rh. The catalysts were characterized by N2-physisorption and COchemisorption to get the information about specific surface area and metal dispersion and size. Finally, the performance of the catalysts in the CO2 methanation reaction was tested and compared with Rh/ceria catalysts with Rh weight percentage of 1, 2, 3 wt.% and doped Rh cerium oxides with Rh content of 0.5, 2.5, 5.5 wt.%.