SO2-induced surface defects on monatomic Ce-doped MoTiOx catalyst for efficient reduction of NOx with NH3

Despite SO 2 being recognized as a catalyst poisoning substance, a trace amount can enhance the acidity of the NH 3 -SCR (selective catalytic reduction) catalyst, which facilitates NH 3 adsorption and accelerates the reaction rate according to the Eley-Rideal mechanism. In this study, monoatomically dispersed Ce atoms were doped into the MoTiO x lattice to regulate the quantity and distribution of sulfate. This regulation was achieved by leveraging the stronger affinity of SO 2 to Ce, thus maximizing the acidifying effect of SO 2 to boost the NH 3 -SCR performance of the catalyst. The catalyst demonstrated the ability to maintain over 80 % NO x conversion for at least 144 hours in the presence of high concentration SO 2 (250 ppm). A detailed examination of the surface dynamics after SO 2 introduction revealed that NH 4 (SO 4 ) 2 , formed on the surface, converted to NH 4 HSO 4 . The decomposition of NH 4 HSO 4 extracted lattice oxygen from the catalyst, leading to an increase in oxygen vacancies on the catalyst surface as the duration of SO 2 exposure increased. The surface-adsorbed oxygen, brought about by these oxygen vacancies, was readily activated, which promoted the dehydrogenation process of NH 3 and the progression of NH 3 -SCR. Further, based on the discovery of the unique phenomenon and mechanism of NH 4 HSO 4 decomposition that generates oxygen vacancies, gases containing poisonous SO 2 were utilized for the pretreatment of the catalyst to optimize its surface and enhance its sulfur resistance (fighting poison with poison). The results demonstrated that the pretreated catalyst rapidly achieved optimal NO x conversion and maintained catalytic stability for over 240 h even in the presence of 250 ppm SO 2 without any decrease in activity. This research innovatively leveraged the poisonous SO 2 to optimize the catalyst's surface, thereby achieving higher catalytic performance and sulfur resistance, which offers valuable insights into the design of novel sulfur-resistant catalysts.