Effect of additives on the structure characteristics, thermal stability, reducibility and catalytic activity of CeO₂–ZrO₂ solid solution for methane combustion

Abstract

M_yO_x-modified CeO₂–ZrO₂ (M = Al, Ba, Cu, La, Nd, Pr, Si) solid solutions with the atomic ratio of Zr/Ce = 1 were prepared by the reverse microemulsion method, and the effect of different additives on the structure characteristics, thermal stability, reducibility, and catalytic activity of CeO₂–ZrO₂ solid solution for methane combustion were investigated. According to their different effects, M_yO_x can be classified into three groups. The first group includes SiO₂ and Al₂O₃ which do not vary the crystalline phase of CeO₂–ZrO₂ solid solution but distort the crystal lattice obviously. They are the most effective additives for improving the surface area, thermal stability, and reducibility of CeO₂–ZrO₂, and they can also promote the catalytic activity of Pd/CeO₂–ZrO₂ for methane combustion. The second group includes La₂O₃, Pr₂O₃, and Nd₂O₃, which can also keep the same crystalline phase, distort the crystal lattice, and improve the surface area and thermal stability of the solid solution, but their effects are much weaker and they decrease the reducibility of the solid solution. The third group includes BaO and CuO, whose effects on the property of CeO₂–ZrO₂ are much different. BaO and CuO, especially CuO, can decrease the thermal stability, and reduction extent of CeO₂–ZrO₂. CuO-modified CeO₂–ZrO₂ calcined at 550 °C shows the comparable high activity for the methane combustion, but after being calcined at 900 °C, CuO-modified CeO₂–ZrO₂ would separate into three phases as CeO₂, ZrO₂, and CuO, resulting in the much lower activity for the methane catalytic combustion.