High N₂ selectivity in selective catalytic reduction of NO with NH₃ over Mn/Ti–Zr catalysts

Abstract

A series of Mn-based catalysts were prepared by a wet impregnation method for the selective catalytic reduction (SCR) of NO with NH 3 . The Mn/Ti-Zr catalyst had more surface area, Lewis acid sites, and Mn 4+ on its surface, and showed excellent activity and high N 2 selectivity in a wide temperature range.

A Review of Low Temperature NH3-SCR for Removal of NOx

“…However, all the catalysts showed poor tolerance to SO2 and SO2/H2O that caused irreversible deactivation. Similar findings were also observed by Zhang et al [111] over the Mn/Ti, Mn/Zr, and Mn/Ti-Zr catalysts, in which Mn/Ti-Zr sample exhibited an excellent NH3-SCR performance in a wide temperature range due to its high surface area, Lewis acid sites, and surface Mn 4+ ions. Figure 16, the Mn-, V-, Cr-, and Cu-oxide confined titania nanotubes had excellent low-temperature activity and meanwhile, vanadium oxide confined titania nanotubes showed a broad operation temperature window for the NH 3 -SCR reaction.…”

“…Although the MnO x /TiO 2 catalyst exhibited excellent resistance to H 2 O, it was deactivated in the presence of SO 2 and SO 2 /H 2 O. Jia et al [110] reported the low-temperature NH 3 -SCR efficiency of MnO x /TiO 2 , MnO x /ZrO 2 , and MnO x /ZrO 2 -TiO 2 catalysts, and found that MnO x /ZrO 2 -TiO 2 obtained good activity at a temperature of 80-360 • C and excellent resistance to H 2 O at 200 • C. However, all the catalysts showed poor tolerance to SO 2 and SO 2 /H 2 O that caused irreversible deactivation. Similar findings were also observed by Zhang et al [111] over the Mn/Ti, Mn/Zr, and Mn/Ti-Zr catalysts, in which Mn/Ti-Zr sample exhibited an excellent NH 3 -SCR performance in a wide temperature range due to its high surface area, Lewis acid sites, and surface Mn 4+ ions. Carbon nanotubes (CNTs) have been reported as promising catalyst support for NH3-SCR catalysis due to their excellent stability and unique electronic and structural properties [36,[112][113][114][115].…”

Deposition of Selective Catalytic Reduction Coating on Wire-Mesh Structure by Atmospheric Plasma Spraying

“…When the temperature was further increased, these active components would rapidly lose their activity, resulting in a sudden decrease of conversion efficiency. Moreover, N 2 selectivity is another standard to evaluate the performance of catalysts, which was influenced by the formation of NO 2 and N 2 O in the reaction [22,30]. During the process of NH 3 -SCR, NO 2 might be generated by the oxidization of NO (5) and (6), moreover NH 3 might be excessively oxidized to N 2 O through the following reactions (6) and (7):NO + O 2 = NO 2 4NH 3 + 4NO + 3O 2 = 4N 2 O + 6H 2 O 4NH 3 + 4NO 2 + O 2 = 4N 2 O + 6H 2 O…”

“…The oxidization of NO would be promoted as temperature increased. Moreover, it was reported that N 2 O is mainly generated via the Eley–Rideal mechanism, which could also be improved as temperature raised [22,30]. These reasons might account for the reduction of N 2 selectivity in the temperature range of 100–450 °C.…”

“…Before the data recording, the reaction gas was purged into the reactor until the NO concentration of the export gas reached the inlet gas concentration (1000 ppm). The data was then recorded for every 50 °C and the NO x conversion efficiency and N 2 selectivity was calculated by the following equation [21,22]. ηNOx=([NOx]in−[NOx]out/[NOx]in)×100%newline[NOx]=[NO]+[N2O]+[NO2] N2 selectivity=[NOx]in−[NOx]out−[NO2]out−[N2O]out[N…”