Studies on the oxidation properties of nanopowder CeO2-based solid solution catalysts for model soot combustion

The catalytic behavior of CeO2-based solid solution catalysts (Ce0.7Zr0.3O2, Ce0.7Pr0.3O2−δ, and Ce0.7Gd0.3O1.85) had been studied for soot combustion. These catalysts were characterized using X-ray diffraction (XRD), UV-visible, Raman, and H2 temperature-programmed reduction (H2-TPR) measurements. The Zr, Pr, and Gd cations replaced Ce cations in the CeO2 lattice to form nanocrystalline CeO2-based solid solutions. The crystallite size of Ce0.7Zr0.3O2, Ce0.7Pr0.3O2−δ, and Ce0.7Gd0.3O1.85 is 7.3, 7.8, and 11.1nm, respectively, which are much smaller than pure CeO2 (36.2nm). The substituting process can promote the formation of oxygen vacancies, which can hasten the diffusion rate of oxygen, then improve the combustion activity. According to the catalytic soot combustion results, the ranking in activity of these catalysts is Ce0.7Zr0.3O2>Ce0.7Pr0.3O2−δ>Ce0.7Gd0.3O1.85∼CeO2, which is well consistent with the reducibility sequence of the samples. The mass of catalyst plus soot mixture have effect on soot combustion: the Tig and Tmax decrease with the increasing of sample weight. Combustion activity of catalysts decreases slowly with cycled runs, which can be attributed to the activity lost of catalyst.