Promoting effect of Ti addition on three-dimensionally ordered macroporous Mn-Ce catalysts for NH3-SCR reaction: Enhanced N2 selectivity and remarkable water resistance

Highlights: • Three-dimensionally ordered macroporous (3DOM) MnCeTi catalysts synthesized. • The 3DOM catalysts have high surface area to expose more active sites. • The addition of Ti promoted the N₂ selectivity. • The MnCeTi catalysts showed remarkable H₂O tolerance. • In situ DRIFT analysis confirmed the SCR reaction followed the L-H mechanism. A series of 3DOM-Mn_xCe_yTi_z catalysts with three-dimensionally ordered macroporous (3DOM) structure were synthesized by a soft template method. The high SCR activity of the 3DOM-Mn₃Ce₁ catalyst at low temperature was owing to the excellent redox ability and rich Lewis and Brønsted acid sites of the catalysts, which were beneficial to improve the catalytic activity. However, the strong oxidizability of MnO_x resulted in the nonselective oxidation of NH₃ and generation of N₂O, decreasing the N₂ selectivity. After addition of Ti, the redox capacity of the 3DOM-Mn₃Ce₁Ti₁ catalyst decreased, and the NH₃ were strongly adsorbed on the acid sites, which enhanced the N₂ selectivity with a broadened temperature window of 240–440 °C and a high GHSV of 120000 h⁻¹. Furthermore, both the 3DOM-Mn₃Ce₁ and 3DOM-Mn₃Ce₁Ti₁ catalysts showed remarkable tolerance of H₂O. Finally, through in situ DRIFT analysis, the Langmuir-Hinshelwood (L-H) mechanism was confirmed as the dominant reaction pathway over the 3DOM-Mn₃Ce₁Ti₁ catalyst.