Sulfur poisoning and regeneration behavior of perovskite-based NO oxidation catalysts

Abstract

SOxuptake and release properties of LaMnO3, Pd/LaMnO3, LaCoO3and Pd/LaCoO3perovskites 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 LaMnO3and LaCoO3significantly increases the sulfur adsorption capacity. Pd/LaMnO3sample accumulates significantly more sulfur than LaMnO3; however it can also release a larger fraction of the accumulated SOxspecies 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 LaCoO3and Pd/LaCoO3is extremely ineffective under similar conditions. However, in the presence of an external reducing agent such as H2(g), Pd/LaMnO3requires much lower temperature (873�K) for complete sulfur regeneration as compared to that of Pd/LaCoO3(973�K). Sequential CO and SOxadsorption 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 SOxas compared to that of the perovskite surface, particularly in the early stages of sulfur poisoning.