De-NO_x Performance and Mechanism of Mn-Based Low-Temperature SCR Catalysts Supported on Foamed Metal Nickel

A series of manganese-based catalysts supported on foamed metal nickel (FMN) with various Mn/Ni ratios was prepared for low-temperature selective catalytic reduction (SCR) of NO with NH₃ (NH₃-SCR). The effects of calcination temperature, amount of added Mn, optimal operating conditions, and H₂O on the elimination of nitrogen oxides (de-NO_x) performance of catalysts were studied. The catalysts were characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and temperature-programmed desorption experiments of NH₃ analyses. The experimental results revealed that the Mn_7.5/FMN catalyst calcined at 350 ºC exhibited the best NO conversion that was ca. 100% at 120-200 ºC. Moreover, it had excellent H₂O tolerance. The superior activity of the Mn_7.5/FMN catalyst, which was calcined at 350 ºC, was attributed to the presence of amorphous manganese oxide, more unsaturated Ni atoms and structural defects, an increase in NH₃ adsorbance, and the number of surface acid sites. Based on these studies, we established that the reaction of the NH₃-SCR with Mn_7.5/FMN catalyst mainly exhibits an Eley-Rideal mechanism.

Keywords:
de-NO_x; low-temperature SCR; MnO_x; foamed metal nickel; mechanism