Dual role of Mn in regulating structural and functional sites of Ag-based catalysts for selective catalytic oxidation of high-concentration NH₃

Abstract

Ammonia fuel, as a promising zero-carbon energy carrier, faces environmental challenges due to high-concentration NH₃ slip in exhaust emissions. Here we develop an efficient Ag-Mn/Al₂O₃ bimetallic catalyst for NH₃ selective catalytic oxidation (NH₃-SCO). Mechanistic investigations reveal the dual role of Mn in this catalytic system: On one hand, Mn preferentially occupies the hydroxyl anchoring sites on Al₂O₃ surface, inducing Ag species aggregation to form nanoparticles with superior O₂ activation capability; on the other hand, highly dispersed Mn species provide abundant Lewis acid sites, significantly enhancing NH₃ adsorption and activation. Through this synergistic effect, the 2Ag3Mn/Al₂O₃ catalyst achieves complete conversion of 7.5 mg/L NH₃ at 300 °C. Further studies demonstrate a distinct temperature-dependent effect on the catalyst’s reaction mechanism, transitioning from –NH-dominated pathway at low temperatures to i-SCR mechanism at high temperatures. This work not only elucidates the mechanism of Mn’s dual role in structural regulation and functional sites but also provides new insights into the rational design of efficient NH₃-SCO catalysts.

Graphical abstract

Keywords

High concentration NH₃-SCO / O₂ activation site / Acid site / Reaction mechanism.

Highlight

	● Optimized Ag/Mn ratio boosts the catalytic oxidation of high concentration NH3.
	● Bimetallic catalyst enhanced ability of O2 activation and NH3 adsorption.
	● The reaction mechanism of the catalyst differs at various temperatures.
	● Mn regulates Ag-based catalysts’ structural and functional sites.

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