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

MyOx-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, MyOx 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.