Co₃O₄Catalysts Modified By Rare Earths And Sn For CO And CH₄Catalytic Oxidation

Catalytic oxidation has been proved to be one of the most effective way to abateCO and CH4pollution in air atmosphere, and also an effective way to make good useof natural gas. So far, the supported precious metal catalysts are still the most activecatalysts for CO and CH4oxidation. However, due to various limitations of theprecious metal catalysts, e.g., the limited availability of precious metals, seekingnon-precious metal catalysts with excellent catalytic activity and stability attracts stillpeople’s attention. Co3O4, as a non-precious metal oxide, is of special interest due toits high catalytic activity for CO and CH4catalytic oxidation.A series of Co3O4spinel catalysts modified by Sm were prepared by theco-precipitation method and tested for CH4and CO oxidation. The catalysts werecharacterized by N2-BET, XRD, TGA-DSC, H2-TPR and XPS techniques. Theaddition of a small amount of Sm into Co3O4leads to an improvement in the catalyticactivity for both reactions. The addition of a small amount of Sm results in theformation of spinel Co3O4and amorphous SmCoO3, hence increasing the number ofCo3+, the active sites, and the active surface oxygen species, which is believed to beresponsible for the improvement of the activity. Co0.95Sm0.05catalyst shows not onlyhigh thermal stability and activity but also good reaction durability in the presence of5%water vapor for CH4oxidation. However, the optimal Co0.90Sm0.10catalyst is stillrapidly deactivated at110oC in the presence of5%water vapor for CO oxidation. Inaddition, the Co0.95Ln0.05catalysts modified by other rare earth metals (Ln=La, Ce,Y, Pr, Nd) were also systematically investigated. The addition of a small amount ofrare earth metals into Co3O4leads to an improvement in the catalytic activity for bothreactions, among which Co0.95Ce0.05, Co0.95Y0.05catalysts show the similar and thehighest activity for CO oxidation. In comparison, Co3O4modified by different rareearth metals shows the similar activity for CH4oxidation.To improve the water-resistant of Co3O4-based catalysts, a series of Co3O4spinelcatalysts modified by Sn were prepared by the co-precipitation method and tested forCH4and CO oxidation. The catalysts were characterized by N2-BET, XRD, TGA-DSC, H2-TPR, XPS and FT-IR techniques. Compared with Co3O4, the additionof a small amount of Sn does not decrease the activity of the catalysts. However,further increasing the amount of Sn could degrade the activity, but the waterresistance of the catalysts has been improved. Phase analysis indicates that theaddition of Sn into Co3O4leads to the formation of SnO2and Co3O4. SnO2generallyhas lower activity than Co3O4. Apparently, the addition of Sn dilutes the highly activeCo sites, thus decreasing the activity. FTIR results demonstrated that the addition ofSn into Co3O4significantly suppresses the adsorption of water molecules on thecatalysts, which is believed to be the major reason for the improved water resistanceof the Sn-modified catalysts.