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. Co0.98Sm0.02 and Co0.95Sm0 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 degrees C. In contrast, Co0.90Sm0.10 was the most active sample for CO oxidation, with CO complete conversion at 120 degrees C. The catalysts were characterized by techniques of N-2 adsortion-desorption with Brunauer-Emmett-Teller technique (N-2-BET), X-ray powder diffraction (XRD), thermal gravity analysis-differential scanning calorimetry (TGA-DSC), H-2 temperature programmed reduction (H-2-TPR) and X-ray photoelectron spectroscopy analysis (XPS). Compared with pure Co3O4, for Co1-xSmx 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. Co0.95Sm0.05 catalyst showed not only high thermal stability and activity but also good reaction durability in the presence of 5% water vapor for CH4 oxidation.