Structure and Catalytic Performance of Manganese-based Mullite-type Mixed Oxides REMn2O5 for Methane Complete Oxidation
Manganese-based mullite-type mixed oxides REMn2O5(RE=Pr,Sm,Eu,Y)catalysts were prepared by a sol-gel method,and their catalytic activities for methane oxidation before and after the loading of palladium were evaluated.The results show that Pd/SmMn2O5 and Pd/YMn2O5 perform the optimized activities with the T50 of 308 and 369 ℃,respectively,which are better than most of the reported noble metal-based catalysts.XRD analysis and DFT calculations demonstrate that the ionic radii of rare earth elements have a significant effect on the crystal structure of mullite,and only those with appropriate ionic radii(Sm,r=0.1079 nm;Eu,r=0.1066 nm)can form mullite phase readily.Due to the large ionic radius of Pr(r=0.1126 nm),perovskite oxides phase noticeably appears in the PrMn2O5 sample.With small ionic radius of Y(r=0.1019 nm),perovskite and manga-nese oxide phases also form in addition to the mullite.There is aboundant lattice oxygen with high mobility in the prepared manganese-based mullites.Strong interactions between Pd species and the mulites result in high dispersion of Pd and the enhanced reducibility of lattice oxygen in mullite,which further promote the catalytic activity for methane oxidation.
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