| Abstract: A series of Ce1-XMnXO2-a-T (X=0.0, 0.1, 0.2, 0.3, 0.5, 0.7, 0.9, 1.0; T stands for calcination temperature, T=500, 650, 800 ℃) mixed oxide catalysts were prepared by hydrothermal method, and the obtained materials were used for methane catalytic combustion. XRD, N2 adsorption/desorption, TG-DSC, UV-Vis-DRS and TPR techniques were applied to study physical-chemical properties of the materials. The results show that, for Ce1-XMnXO2-a-500 calcined at 500 ℃, all catalysts are with relatively high surface area and the maximal substitution value of Mn introduced into CeO2 crystal lattice forming homogeneous solid solution is 0.7, while Mn2O3 phase emerged if X> 0.7. The maximal substitution value of Mn decreased with the enhancement of calcination temperature, which is 0.5 and 0.3 at the temperatures of 650 and 800 ℃, respectively. At the same time, the surface area of catalysts also decreased with the increase of calcination temperature. Three stages of reduction were observed on Ce1-XMnXO2-a-800 from TPR profiles. Firstly Mn2O3 was reduced into Mn3O4 at 340～420 ℃, then Mn3O4 was reduced into MnO at 420～480 ℃ and finally bulky CeO2 was reduced at 700～900 ℃. Catalytic activity was determined by catalyst composition, reduction ability and calcination temperature. The surface area of catalysts was not the main factor to influence catalytic activity of methane combustion. Ce0.3Mn0.7O2-a-800 obtained relatively high activity. The temperature for 10% and 90% methane conversion was 403 and 613 ℃, respectively. Further study showed that, catalytic activity of Ce0.3Mn0.7O2-a catalyst decreased with the increase of calcination temperatures (500, 650, 800 and 1 000 ℃). |
