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 NH3SCR of NO. However, Mn-based catalysts still suffer from some drawbacks, such as poor N-2 selectivity and narrow operating temperature window. Methods: Herein, MnTiOx catalyst was synthesized through a facile coprecipitation method. Ce was adopted to partially substitute Mn in MnTiOx catalyst to promote N-2 selectivity and high-temperature activity. Significant findings: The partial substitution of Mn by Ce in MnTiOx catalyst could significantly improve N-2 selectivity and widen operating temperature window. The higher substitution rate of Mn by Ce was, the better N-2 selectivity of Ce MnTiOx 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 N-2 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. (C) 2022 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Automated summary

This study synthesized MnTiOx catalyst by partially replacing Mn with Ce, and found that the substitution of Mn with Ce could significantly improve the N-2 selectivity and widen the operating temperature window of the catalyst. The substitution also influenced the redox property and surface acidity of the catalyst, promoting N-2 formation and effectively restraining N2O formation in NH3-SCR reaction.