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Spinel-structured Mn–Ni nanosheets for NH3-SCR of NO with good H2O and SO2 resistance at low temperature

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Abstract

Novel Mn–Ni spinel nanosheets were investigated for the NH3-SCR of NO at low temperature by urea-hydrolysis (UH) and urea-hydrolysis hydrothermal-synthesis (UHHS), and compared with co-precipitation hydrothermal synthesis (CPHS) and co-precipitation (CP) methods. The optimum molar ratio of Mn/Ni (2 : 1) and urea/(Mn + Ni) (3 : 1) were determined, as also were the suitable hydrothermal temperature (130 °C for 24 h) and further calcination (450 °C for 6 h). An Mn(2)Ni(1)Ox-UHHS catalyst produced a purer spinel-structured NiMn2O4 nanosheet than Mn(2)Ni(1)Ox-UH, both of which showed highly efficient SCR activity (>98% NOx conversion at 100–250 °C) and N2 selectivity (>95% at <150 °C and >85% at <250 °C). The NiMn2O4-UHHS nanosheet also exhibited excellent resistance to H2O and SO2 in the low-temperature range (85–90% NOx conversion at 150–300 °C with 10 vol% H2O and 150 ppm SO2). Characterization with BET, TPD, TPR, XPS SEM-EDS, TGA, AXNES and DRIFTS indicated that the main reasons for the excellent activity and resistances were the high specific surface area, greater NH3 adsorption ability and more efficient electronic interaction (Mn3+ + Ni3+ ↔ Mn4+ + Ni2+) of active octahedral-sites in the [Ni2+Mn4+]tet[Ni2+Ni3+Mn3+Mn4+]octO4 spinel structure with an outside configuration of tetrahedrons embedded with Ni which avoided the sulfation of the inside octahedron-wrapped Mn active sites, and the nanosheet morphology which retarded the adhesion of sulfur ammonia species, resulting in the remission of deposition/inhibition effects. The reaction pathways were based on ER mechanisms via gaseous NO with adsorbed NH3-species and also the LH-then-ER mechanisms through the combination of bidentate nitrate with coordinated NH3/NH4+, which were less affected by SO2 competitive adsorption, attributed to be a major reason for good SO2-resistance.

Graphical abstract: Spinel-structured Mn–Ni nanosheets for NH3-SCR of NO with good H2O and SO2 resistance at low temperature

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Article information


Submitted
03 Jul 2020
Accepted
15 Aug 2020
First published
21 Aug 2020

Catal. Sci. Technol., 2020, Advance Article
Article type
Paper

Spinel-structured Mn–Ni nanosheets for NH3-SCR of NO with good H2O and SO2 resistance at low temperature

F. Gao, X. Tang, Z. Sani, H. Yi, S. Zhao, Q. Yu, Y. Zhou, Y. Shi and S. Ni, Catal. Sci. Technol., 2020, Advance Article , DOI: 10.1039/D0CY01337D

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