Abstract:
It is a challenge to develop highly sulfur dioxide and water (SO
2+H
2O) 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@CeO
2 and CeO
2/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@CeO
2 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 CeO
2/Ce-OMS-2 catalyst, large amounts of CeO
2 deposited on the surface of Ce-OMS-2 and blocked the mesoporous structure. Furthermore, SO
2 reacted with CeO
2/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 CeO
2/Ce-OMS-2 catalyst exhibited the low SCR activity and poor SO
2+H
2O tolerance during the SCR reaction. We also clarify the reason for the anti-sulfur of core-shell Ce-OMS-2@CeO
2 catalyst. In the presence of SO
2 and H
2O, SO
2 could easily react with NH
3 and H
2O to produce ammonium bisulfate (NH
4HSO
4, ABS) on the surface of the Ce-OMS-2 and CeO
2/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@CeO
2 catalyst, the formed ABS could significantly 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@CeO
2 catalyst. A dynamic balance of ABS formation and decomposition was achieved over Ce-OMS-2@CeO
2 even at low temperatures, which hindered the SO
2 poisoning during the NH
3-SCR reaction. As expected, the core-shell Ce-OMS-2@CeO
2 catalyst showed excellent SCR performance and SO
2+H
2O resistance (~100% NO conversion in the temperature range of 100−200 ℃ without SO
2, ~80% NO conversion for 4 h in the presence of SO
2). This work provides an effective strategy for the development of efficient and stable Mn-based low-temperature SCR catalysts.