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Exhaust gas aftertreatment systems play a key role in controlling transportation greenhouse gas emissions. Modern aftertreatment systems, often based on Pd metal supported on aluminum oxide, provide high catalytic activity but are vulnerable to sulfur poisoning due to formation of inactive sulfate species. This paper focuses on regeneration of Pd-based catalyst via the decomposition of alumina-supported aluminum and palladium sulfates existing both individually and in combination. Decomposition experiments were carried out under hydrogen (10% H2/Ar), helium (He), low oxygen (0.1% O2/He), and excess oxygen (10% O2/He). The structure and composition of the model catalysts were examined before and after the decomposition reactions via powder X-ray diffraction and elemental sulfur analysis. The study revealed that individual alumina-supported aluminum sulfate decomposed at a higher temperature compared to individual alumina-supported palladium sulfate. The simultaneous presence of aluminum and palladium sulfates on the alumina support decreased their decomposition temperatures and led to a higher amount of metallic palladium than in the corresponding case of individual supported palladium sulfate. From a fundamental point of view, the lowest decomposition temperature was achieved in the presence of hydrogen gas, which is the optimal decomposition atmosphere among the studied conditions. In summary, aluminum sulfate has a two-fold role in the regeneration of a catalyst—it decreases the Pd sulfate decomposition temperature and hinders re-oxidation of less-active metallic palladium to active palladium oxide.

One way to lower CO 2 and other harmful emissions of the transportation sector is the development of natural gas fueled vehicles. Availability of natural gas is good, and it is easy to apply to stoichiometric and lean-burn engines, which makes it ready-to-use technology. The main concern in the field is a sulfur poisoning of the exhaust gas after treatment system. We aim to clarify mechanisms of sulfur poisoning and regeneration of a lean-burn methane oxidation catalyst. Overall, it is concluded that sulfur itself is not the only reason for the deactivation of methane oxidation catalyst, but it is a joint effect of water vapor and sulfur species. The irreversible sulfur poisoning deteriorates oxygen mobility and hinders water desorption, which inhibits low temperature methane oxidation activity. The regeneration of sulfur poisoned catalyst takes place stepwise: PdSO 4 → PdSO 3 + 0.5O 2 → Pd + SO 2 + 0.5O 2 . The formation of metallic palladium makes the catalyst vulnerable for sintering, which leads to deactivation during long-term regeneration. [ABSTRACT FROM AUTHOR]