Promotional effects of samarium on Co3O4 spinel for CO and CH4 oxidation

A series of Co₃O₄ spinel catalysts modified by Sm were prepared by co-precipitation method and tested for CH₄ and CO oxidation. The addition of a small amount of Sm into Co₃O₄ led to an improvement in the catalytic activity for both reactions. Co_0.98Sm_0.02 and Co_0.95Sm_0.05, the two samples with Co/Sm molar ratio of 0.98/0.02 and 0.95/0.05 in sequence, showed the similar and the highest activity for CH₄ oxidation, with CH₄ complete conversion at 450 °C. In contrast, Co_0.90Sm_0.10 was the most active sample for CO oxidation, with CO complete conversion at 120 °C. The catalysts were characterized by techniques of N₂ adsortion-desorption with Brunauer-Emmett-Teller technique (N₂-BET), X-ray powder diffraction (XRD), thermal gravity analysis-differential scanning calorimetry (TGA-DSC), H₂ temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy analysis (XPS). Compared with pure Co₃O₄, for Co_1–xSm_x catalysts with 0.02≤x≤0.10, the addition of a small amount of Sm resulted in the formation of spinel Co₃O₄ and amorphous SmCoO₃, hence increasing the number of Co³⁺ and the active surface oxygen species, which was responsible for the improvement of the activity. Co_0.95Sm_0.05 catalyst showed not only high thermal stability and activity but also good reaction durability in the presence of 5% water vapor for CH₄ oxidation.