Sulfur Poisoning and Regeneration Behavior of Perovskite-Based NO Oxidation Catalysts

SOx uptake and release properties of LaMnO3, Pd/LaMnO3, LaCoO3 and Pd/LaCoO3 perovskites were investigated via in situ Fourier transform infrared (FTIR) spectroscopy, temperature programmed desorption and X-ray photoelectron spectroscopy. Sulfation of the perovskite leads to the formation of surface sulfite/sulfate and bulk-like sulfate species. Pd addition to LaMnO3 and LaCoO3 significantly increases the sulfur adsorption capacity. Pd/LaMnO3 sample accumulates significantly more sulfur than LaMnO3; however it can also release a larger fraction of the accumulated SOx species in a reversible fashion at elevated temperatures in vacuum. This is not the case for Co-based materials, where thermal regeneration of bulk sulfates on poisoned LaCoO3 and Pd/LaCoO3 is extremely ineffective under similar conditions. However, in the presence of an external reducing agent such as H2 (g), Pd/LaMnO3 requires much lower temperature (873 K) for complete sulfur regeneration as compared to that of Pd/LaCoO3 (973 K). Sequential CO and SOx adsorption experiments performed via in situ FTIR indicate that in the presence of carbonyls and/or carbonates, Pd adsorption sites may have a stronger affinity for SOx as compared to that of the perovskite surface, particularly in the early stages of sulfur poisoning.