A Study On The Manganese-based Oxide Catalysts Used For The Catalytic Oxidation Of CO And C₃H₈ At Low Temperature

1,A series of La-Mn-Ce-O mixed oxide catalysts with various atomic ratios (La+Mn/La+Mn+Ce) and different calcination temperatures were prepared by the citric acid complexation-organic template decomposition method. During the synthesis, the citric acid and the cetyltrimethylammoniumbromide (CTABr) were used as the coordination agent and the organic template, respectively. It gave rise to a clear solution of soluble homogeneous mixed metal oxides containing a cationic surfactant in acidic medium, which was precipitated in basic medium, and followed by hydrothermal treatment. The catalysts were characterized by using the physisorb of N2, XRD, XPS, H₂-TPR techniques, etc. The results of physisorb of N2 show that the samples possess high BET surface areas and uniform mesoporous structure. The pore diameter of the sample is mainly between 36.8?～38.7?. Combining the results of XPS and H₂-TPR, it is concluded that besides the surface area, the number of the adsorbed oxygen species on the surface, the oxygen-transferring ability of CeO2, the ease of the activation of Mn-O bond and the surface atomic percentages of La, Mn and Ce are the crucial factors for the redox properties of the catalyst. The more the surface atomic ratio of La:Mn:Ce , the better catalytic synergetic effect is show . The sample with the atomic ratio of La+Mn/La+Mn+Ce=0.5, calcined at 500℃possesses the highest oxidation activity, the temperatures for the complete oxidation of CO and C₃H₈ on this sample are 160℃and 320℃, respectively. Additionally, the samples prepared by the citric acid complexation-organic template decomposition method, show strong ability to prevent the sintering and poisoning by SO2.2,The catalysts of manganese oxides supported on Al₂O₃,SiO₂ and MgO were prepared by impregnation method. The catalysts were characterized by means of XRD, XPS, H₂-TPR and Mn K-edge EXAFS. Their catalytic behavior for CO oxidation was evaluated. The XRD results show that the manganese oxide species are highly dispersed on Al₂O₃ and SiO₂ supports, while on MgO support, a stable complex oxide phase, namely Mg6MnO8, was detected by XRD. The results of XAFS analysis suggest that on Al₂O₃ and SiO₂ supports manganese exists mainly in the form of highly dispersed Mn2O3. Combining the results of XPS and H₂-TPR, the extent for the metal-support interaction on different supports follows the sequence: MnOx/MgO> MnOx/Al₂O₃>MnOx/SiO₂, a typical support effect for manganese oxide catalysts is...