Mechanistic insight into the promoting effect of partial substitution of Mn by Ce on N2 selectivity of MnTiOx catalyst for NH3-SCR of NO

Background

Owing to excellent low-temperature activity and environmentally friendliness, Mn-based catalyst is commonly considered as one of the promising alternatives to traditional V-based catalysts for NH₃-SCR of NO. However, Mn-based catalysts still suffer from some drawbacks, such as poor N₂ selectivity and narrow operating temperature window.

Methods

Herein, MnTiO_x catalyst was synthesized through a facile coprecipitation method. Ce was adopted to partially substitute Mn in MnTiO_x catalyst to promote N₂ selectivity and high-temperature activity.

Significant findings

The partial substitution of Mn by Ce in MnTiO_x catalyst could significantly improve N₂ selectivity and widen operating temperature window. The higher substitution rate of Mn by Ce was, the better N₂ selectivity of Ce MnTiO_x catalyst was. Partial substitution of Mn by Ce led to mild redox property, enhanced surface acidity, lower surface Mn⁴⁺ and chemisorbed oxygen species proportion on catalyst surface. Besides, partial substitution of Mn by Ce was in favor of the generation NH₄NO₂ species in NH₃ oxidation reaction, and boosted the consumption of -NH₂ species during NH₃-SCR reaction, which was conducive to N₂ formation. The reactions between adsorbed NH₃ species and oxygen species through Langmuir-Hinshelwood mechanism might be inhibited by partial substitution of Mn by Ce, thus effectively restraining N₂O formation.