A Highly Effective Catalyst of Sm-MnOx for the NH3-SCR of NOx at Low Temperature: Promotional Role of Sm and Its Catalytic Performance

Sm-Mn mixed oxide catalysts prepared by the coprecipitation method were developed, and their catalytic activities were tested for the selective catalytic reduction (SCR) of NO with ammonia at low temperature. The results showed that the amount of Sm markedly influenced the activity of the MnO x catalyst for SCR, that the activity of the Sm-Mn mixed oxide catalyst exhibited a volcano-type tendency with an increase in the Sm content, and that the appropriate mole ratio of Sm to Mn in the catalyst was 0.1. In addition, the presence of Sm in the MnO x catalyst can obviously enhance both water and sulfur dioxide resistances. The effect of Sm on the physiochemical properties of the Sm-MnO x catalyst were investigated by XRD, low-temperature N 2 adsorption, XPS, and FE-SEM techniques. The results showed that the presence of Sm in the Sm-MnO x catalyst can restrain the crystallization of MnO x and increase its surface area and the relative content of both Mn 4+ and surface oxygen (O S ) on the surface of the Sm-MnO x catalyst. NH 3 -TPD, NO-TPD, and in situ DRIFT techniques were used to investigate the absorption of NH 3 and NO on the Sm-MnO x catalyst and their surface reactions. The results revealed that the presence of Sm in the Sm 0.1 -MnO x catalyst can increase the absorption amount of NH 3 and NO on the catalyst and does not vary the SCR reaction mechanism over the MnO x catalyst: that is, the coexistence of Eley–Rideal and Langmuir–Hinshelwood mechanisms (bidentate nitrate is the active intermediate), in which the Eley–Rideal mechanism is predominant.