Improved N₂ Selectivity of MnO_x Catalysts for NO_x Reduction by Engineering Bridged Mn³⁺ Sites

Abstract

Mn-based catalysts are promising for selective catalytic reduction (SCR) of NO x with NH 3 at low temperatures due to their excellent redox capacity. However, the N 2 selectivity of Mn-based catalysts is an urgent problem for practical application owing to excessive oxidizability. To solve this issue, we report a Mn-based catalyst using amorphous ZrTiO x as the support (Mn/ZrTi-A) with both excellent low-temperature NO x conversion and N 2 selectivity. It is found that the amorphous structure of ZrTiO x modulates the metal−support interaction for anchoring the highly dispersed active MnO x species and constructs a uniquely bridged Mn 3+ bonded with the support through oxygen linked to Ti 4+ and Zr 4+ , respectively, which regulates the optimal oxidizability of the MnO x species. As a result, Mn/ZrTi-A is not conducive to the formation of ammonium nitrate that readily decomposes to N 2 O, thus further increasing N 2 selectivity. This work investigates the role of an amorphous support in promoting the N 2 selectivity of a manganese-based catalyst and sheds light on the design of efficient low-temperature deNO x catalysts.

Catalytic Ozonation of Low Concentration Toluene over MnFeOx-USY Catalyst: Effects of Interactions between Catalytic Components and Introduction of Gas Phase NOx

“…On the surface of MnFeO x -USY, the adsorption peaks at ∼1410 and 1150 cm −1 were assigned to bulk ionicnitrate and bridged nitrate species, respectively, 39,41−43 and the bands at near 1260 and 1550 cm −1 were attributed to monodentate nitrate species. 39,44,45 The vibration peak of bidentate nitrate species at 1600 cm −1 appeared on the surface of other four catalysts except MnFeO x -USY, 14,39 and the peak intensity followed the order of MnFeO x > FeO x -USY > MnO x -USY > USY. What's more, apart from bidentate nitrate species, there were other kinds of nitrate species on the MnFeO x and FeO x -USY surface.…”

Modification of Recycled Industrial Solid Waste Incineration Fly Ash as a Low-cost Catalyst for NOx Removal

“…7 for RFA, FA/Mg-10%, FA/Ti-10%, and FA/Zr-10% were examined to explore the acid site characteristics in modified fly ash catalysts with varying crystallinities. The peaks observed at 1605 cm -1 , 1574 cm -1 , and 1444 cm -1 indicate the presence of Lewis acids, while the peak at 1547 cm -1 corresponds to Brønsted acids, and another peak at 1477 cm -1 suggests the coexistence of Lewis and Brønsted acids (Si et al, 2022;Che et al, 2023). Notably, the enhanced acidity of FA/Zr-10% surpasses that of other modified fly ash catalysts (such as FA/Mg-10% and FA/Ti-10%).…”

“…This decrease may be attributed to the increased production of H2O, which affects the reduction of the catalyst's active surface at higher temperatures, thereby reducing the selectivity for N2. Additionally, the decline in N2 selectivity is also due to the heightened oxidation capability of NO to NO2, strongly influencing the catalyst's selectivity (Che et al, 2023).…”

Insights into the Acidic Site in Manganese Oxide in Terms of the Sulfur and Water Tolerance of Low-Temperature NH3 Selective Catalytic Reduction

“…Despite significant success in thermal power stations, managing NO x in nonpower sectors remains a formidable task, primarily due to the intensified interference effects from SO 2 and H 2 O at lower operating temperatures. Under typical low operating temperatures (100–200 °C), V 2 O 5 -WO 3 (MoO 3 )/TiO 2 fails to deliver adequate performance. − Consequently, there is an urgent need to develop SCR catalysts that can provide exceptional denitrification efficiency and robust tolerance to SO 2 and H 2 O within this temperature range.…”