An Efficient Two-Step Method for NH₃ Removal at Low Temperature Using CoO_x-CuO_x/TiO₂ as SCO Catalyst Followed by NiMn₂O₄ as SCR Catalyst

Abstract

A novel two-step method was designed for NH3 removal at low temperature (150–200 °C) in this work. In step 1, the selective catalytic oxidation of NH3 to NO x occurred on the SCO catalyst to make the outlet [NH3]/[NO x ] ≈ 1. In step 2, the selective catalytic reduction of formed NO x by unreacted NH3 occurred on the SCR catalyst, so as to improve the NH3 removal efficiency and N2 selectivity of the whole two-step reaction process. For the step 1 catalyst, a series of TiO2 supported transition metal oxides catalysts were prepared and tested to select the suitable one. The two-step method showed superior catalytic performance with the NH3 removal efficiency higher than 95% as well as the N2 selectivity higher than 85% in 170–180 °C by using 7.5CoO x -7.5CuO x /TiO2 as the step 1 catalyst and NiMn2O4 as the step 2 catalyst. The analysis of the N2O formation indicated that the N2O formation of the two-step method mainly consisted of the N2O formed in step 1 and step 2 catalysts. The N2 selectivity of the two-step method at 150–170 °C can be improved by the following ways: reducing the N2O formed by NH3 oxidation on the step 2 catalyst, increasing the NO x formed on the step 1 catalyst to inhibit the oxidation of NH3 on the step 2 catalyst, and further reducing the N2O formation on the step 1 catalyst.

Molecular-Level Insight into Selective Catalytic Reduction of NOx with NH3 to N2 over a Highly Efficient Bifunctional Va-MnOx Catalyst at Low Temperature

“…or supported MnO x on TiO 2 , − SiO 2 , , Al 2 O 3 , ,, zeolites, − and carbon-based materials. − Improved activity and N 2 selectivity were thus achieved. The second approach is to prepare materials to develop the bifunctional catalysts, which involve the cooperation of two types of active sites with specific properties. − Several bifunctional catalysts that consist of an oxidation component (such as Mn, Mn-Ce, Mn-Cr, Mn-Cu, and Mn/Ce-Zr oxides, ,, CoO x -CuO x /TiO 2 , etc.) and an SCR-active component (such as Fe-ZSM-5, , V 2 O 5 -WO 3 /TiO 2 , Fe-beta, NiMn 2 O 4 , etc.)…”

“…The second approach is to prepare materials to develop the bifunctional catalysts, which involve the cooperation of two types of active sites with specific properties. − Several bifunctional catalysts that consist of an oxidation component (such as Mn, Mn-Ce, Mn-Cr, Mn-Cu, and Mn/Ce-Zr oxides, ,, CoO x -CuO x /TiO 2 , etc.) and an SCR-active component (such as Fe-ZSM-5, , V 2 O 5 -WO 3 /TiO 2 , Fe-beta, NiMn 2 O 4 , etc.) have received attention, in which V-based oxides possess high N 2 selectivity and resistance to sulfur oxide poisoning. , Specifically, vanadates have attracted intense attention due to their higher thermal stability in comparison to V 2 O 5 . − However, vanadates have not been exploited to date as an active component of a bifunctional SCR catalyst. ,,,, Furthermore, the deceptively simple synergism between the oxidation component and the SCR-active component for the bifunctional catalysts still remains elusive at a molecular level .…”

Finely Iron-Dispersed Particles on β Zeolite from Solvated Iron Atoms: Promising Catalysts for NH3-SCO

“…14,15 In the last decades, several catalytic systems have been proposed for this process, such as supported or unsupported noble metals, [16][17][18] transition metal oxides, 16,[19][20][21] and mixed oxides. [22][23][24][25] In particular, iron [26][27][28] and copper [28][29][30][31] oxides have demonstrated to be active and selective catalysts. On the other hand, Fe and Cu resulted to be active and selective species also when encapsulated as ions inside zeolitic frameworks, [31][32][33] probably due to the possibility to work in two different oxidation states (Fe 2+ /Fe 3+ and Cu 2+ /Cu + ).…”

“…The ideal catalyst should be selective and active in a broad temperature range and should possess high water tolerance and very low sensitivity to sulfur poisoning. , In the past decades, several catalytic systems have been proposed for this process, such as supported or unsupported noble metals, − transition-metal oxides, ,− and mixed oxides. − In particular, iron − and copper − oxides have demonstrated to be active and selective catalysts. On the other hand, Fe and Cu demonstrated to be active and selective species also when encapsulated as ions inside zeolitic frameworks − probably due to the possibility to work in two different oxidation states (Fe 2+ /Fe 3+ and Cu 2+ /Cu + ) …”

Progress in selective catalytic oxidation of ammonia to nitrogen

“…也有研究发现, 我国排放氨气 浓度的增加削弱了二氧化硫和氮氧化物的控制对细颗 粒物中硝酸盐减少的效益 [4] . 2018年1月1日 [25,26] 、Ru [27~29] 、Ir [30] 、Au [31] 、Ag 、Co [42,43] 、Mn [44,45] 、V [46,47] [48,49] 、MCM-41型 [50] 、SSZ-13型 [51~53] 和 SAPO-34型 [52,54] 材料上. [62] , 并且分子筛载体具有大的比 表面积和良好的离子交换性质, 允许以高分散形式引 入活性成分 [63,64] , 得到了研究者的广泛研究.…”