| Summary: | Manganese oxide-supported palygorskite (MnO<sub>x</sub>/PG) catalysts are considered highly efficient for low-temperature SCR of NO<sub>x</sub>. However, the MnO<sub>x</sub>/PG catalyst tends to be poisoned by SO<sub>2</sub>. The effect of SO<sub>2</sub> on activity of the SO<sub>2</sub>-pretreated poisoning catalysts under ammonia-free conditions was explored. It was determined that the MnO<sub>x</sub>/PG catalyst tends to be considerably deactivated by SO<sub>2</sub> in the absence of ammonia and that water-washed regeneration can completely recover activity of the deactivated catalyst. Based on these results and characterizations of the catalysts, a reasonable mechanism for the deactivation of MnO<sub>x</sub>/PG catalyst by SO<sub>2</sub> was proposed in this study. SO<sub>2</sub> easily oxidized to SO<sub>3</sub> on the surface of the catalyst, leading to the formation of polysulfuric acid, wrapping of the active component and blocking the micropores. The deactivation of the MnO<sub>x</sub>/PG catalyst is initially caused by the formation of polysulfuric rather than the deposition of ammonia sulfate, which occurs later.
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