Sulfur resistance of Ca-substituted LaCoO3 catalysts in CO oxidation

Abstract

La1-xCaxCoO3 perovskite catalysts were prepared by using citrate sol-gel method with the various calcium ratios (denoted as La1-xCaxCoO3 (x = 0, 0.1, 0.2, 0.3, 0.4)). The prepared catalysts were poisoned with simulated gas including SO2 to investigate the sulfur resistance of the catalysts. The fresh and sulfur-aged catalysts were then applied to CO oxidation reaction. X-ray diffraction analysis revealed that the catalysts containing calcium also showed perovskite structure. La0.8Ca0.2CoO3 showed the highest CO oxidation activity among the Ca-substituted LaCoO3 catalysts. H2 temperature-programmed reduction indicated that the addition of Ca to LaCoO3 promotes the facile reduction of Co3+, which can explain the higher activity for CO oxidation. Surprisingly, small amounts of SO2 poisoning were observed to promote CO oxidation in Ca-substituted catalysts, although further exposure to SO2 gave rise to the decline of catalytic activity. In addition, Ca-substituted catalysts had higher catalytic activity than LaCoO3 after poisoning with small amounts of sulfur. XPS analysis indicated that Ca-substituted catalysts possessed the less amount of sulfate on the surface than LaCoO3 upon SO2 poisoning. It was summarized that La1-xCaxCoO3 perovskite catalysts had stronger resistance to sulfur poisoning and higher catalytic activity for CO oxidation.