Architecture of core-shell Ce-OMS-2@CeO₂ catalyst and its SCR activity and SO₂+H₂O tolerance performance at low-temperature

It is a challenge to develop highly sulfur dioxide and water (SO₂+H₂O) resistance for the low-temperature selective catalytic reduction (SCR) catalysts of nitrogen oxide (NO_x) in the non-electric-power industry. In this paper, core-shell and loaded type of Ce-OMS-2 complexes (Ce-OMS-2@CeO₂ and CeO₂/Ce-OMS-2) were successfully prepared. Their textural properties were characterized and catalytic performance were carried out. The results showed that the core-shell Ce-OMS-2@CeO₂ material could maintain the mesoporous structure and significantly improve the mass transfer and adsorption of the reaction gas NO, thus improving the SCR efficiency. On the contrary, for the loaded CeO₂/Ce-OMS-2 catalyst, large amounts of CeO₂ deposited on the surface of Ce-OMS-2 and blocked the mesoporous structure. Furthermore, SO₂ reacted with CeO₂/Ce-OMS-2 to form lots of metal sulfate (manganese sulfate or cerium sulfate), which led to the deactivation of the active Mn sites. Therefore, the CeO₂/Ce-OMS-2 catalyst exhibited the low SCR activity and poor SO₂+H₂O tolerance during the SCR reaction. We also clarify the reason for the anti-sulfur of core-shell Ce-OMS-2@CeO₂ catalyst. In the presence of SO₂ and H₂O, SO₂ could easily react with NH₃ and H₂O to produce ammonium bisulfate (NH₄HSO₄, ABS) on the surface of the Ce-OMS-2 and CeO₂/Ce-OMS-2 catalysts. Then ABS can be physically deposited on the surface of the catalysts, thus blocking the active Mn sites to participate in the SCR reaction. Interesting, for the core-shell Ce-OMS-2@CeO₂ catalyst, the formed ABS could significantly be decomposed at low temperature, leading to the exposure of surface active Mn sites of the catalyst. Herein, it could maintain the efficient SCR performance over the Ce-OMS-2@CeO₂ catalyst. A dynamic balance of ABS formation and decomposition was achieved over Ce-OMS-2@CeO₂ even at low temperatures, which hindered the SO₂ poisoning during the NH₃-SCR reaction. As expected, the core-shell Ce-OMS-2@CeO₂ catalyst showed excellent SCR performance and SO₂+H₂O resistance (~100% NO conversion in the temperature range of 100−200 ℃ without SO₂, ~80% NO conversion for 4 h in the presence of SO₂). This work provides an effective strategy for the development of efficient and stable Mn-based low-temperature SCR catalysts.