The development of high-efficiency catalysts is the key to the low-temperature NH3-SCR technology. The introduction of SO2 and H2O will lead to poisoning and deactivation of the catalysts, which severely limits the development and application of NH3-SCR technology. This review introduces the necessity of NOx removal, explains the mechanisms of H2O and SO2 poisoning on NH3-SCR catalysts, highlights the Mn-based catalysts of different active metals and supports and their resistance to H2O and SO2, and analyses the relationship between metal modification, selection of support and preparation method, morphology and structure design and SO2/H2O resistance. Given the current problems, this review points out the future research focus of Mn-based catalysts and also puts forward corresponding countermeasures to solve the existing problems.

A review of Mn-based catalysts for low-temperature NH3-SCR: NOx removal and H2O/SO2 resistance.

The effects of Mn-based catalysts on the selective catalytic reduction of NOx with NH3 at low temperature: A review

An in-situ DRIFTs study of Mn doped FeVO4 catalyst by one-pot synthesis for low-temperature NH3-SCR

Fe2O3-based catalysts have promising potential in the selective catalytic reduction (SCR) of NO with NH3 with the advantages of environmental friendliness, excellent medium-high SCR activity, good N2 selectivity, and high SO2 tolerance. However, the NH3-SCR mechanism over Fe2O3-based catalysts remains highly uncertain and controversial due to the complex nature of the SCR reaction. Herein, the NH3-SCR reaction pathways over the α-Fe2O3(012) surface are elucidated at the atomic level by density functional theory calculations and experimental measurements. We demonstrate that, different from the NH3 activation mechanism in numerous SCR catalytic systems, the reaction tends to follow the NO activation mechanism, in which NO activated at Fe sites reacts with NH3 to form a NH2NO intermediate and further decomposes into N2 and H2O, in synchronization with the formation of a surface OH group. Subsequently, the catalyst is regenerated by an O2-assisted surface-dehydrogenation process. The activation of NO as well as the formation of the NH2NO intermediate is the rate-determining step of the complete SCR cycle. This study enhances the atomic-level understanding toward the NH3-SCR reaction and provides insights for the development of Fe2O3-based SCR catalysts.

Reaction Pathways of the Selective Catalytic Reduction of NO with NH3 on the α-Fe2O3(012) Surface: a Combined Experimental and DFT Study.

Inhibition effects of Pb species on the V2O5-MoO3/TiO2 catalyst for selective catalytic reduction of NOx with NH3: A DFT supported experimental study

Quantum chemistry study of SCR-NH3 nitric oxide reduction on Ce-doped γFe2O3 catalyst surface

The low-temperature catalytic NO removal efficiencies of catalysts with two different manganese precursors, manganese acetate (αMA catalyst) and manganese nitrate (αMN catalyst), were compared and studied. The NH3-SCR of NO tests using these catalysts were carried out in a self-made reaction device to measure the catalytic activity of the catalysts. Moreover, the reaction pathway analysis of NH3-SCR of NO on the surface of MnO2/SiO2 catalyst and Mn2O3/SiO2 catalyst were performed based on DFT calculations individually. The experimental results show that the NO conversion of αMN catalyst is higher than the αMA catalyst at low temperature (< 180 °C). Besides, the XRD test shows that the main crystal phase is MnO2 for αMN catalysts, and Mn2O3 for αMA catalyst, and the XPS characterization exhibits that the αMN catalyst has the highest MnO2/Mn2O3 ratio. Moreover, DFT calculations indicate that the decompositions of NH2NO and NHNO are the rate determining steps in the whole NH3-SCR of NO process and the decomposition activation energy of NH2OH and NHNO on MnO2 is lower than that on Mn2O3. This is the main reason for the higher NO conversion of catalyst prepared with manganese nitrate as precursor at low temperature.

The effects of manganese precursors on NO catalytic removal with MnOx/SiO2 catalyst at low temperature

Based on the density functional theory, the adsorption processes of NH3, and NO and O2 on the Mn active sites of MnOx/SiO2 β-cristobalite (101) surface were simulated. The results show that NH3, NO and O2 can be effectively adsorbed on the Mn active sites of both MnO2/SiO2 β-cristobalite (101) and Mn2O3/SiO2 β-cristobalite (101) surface. The adsorption characteristics of the two catalysts are different. The adsorption energy of NH3 molecule on the MnO2/SiO2 β-cristobalite (101) surface is much higher than that on the Mn active sites of Mn2O3/SiO2 β-cristobalite (101) surface. The NO molecule and the O2 molecule are a little easier to be adsorbed on the Mn active sites of Mn2O3/SiO2 β-cristobalite (101) surface. The large difference of NH3 adsorption energy between the two catalysts becomes one of the main reasons why MnO2/SiO2 has better catalytic activity than Mn2O3/SiO2. Furthermore, the high adsorption energy of NH3 on MnO2/SiO2 surface proves that SiO2 is an excellent carrier and MnO2/SiO2 catalyst is an outstanding NH3-SCR catalyst at low temperature.

Understanding the adsorption of NH 3 , NO and O 2 on the MnO x /SiO 2 β-cristobalite (101) surface with density functional theory

The catalytic NO removal efficiencies of MnFeOx/SiO2 catalysts with different Fe/Si were compared and studied. The reaction pathway analysis of NH3-SCR on the surface of MnFeOx/SiO2 catalyst was performed based on DFT calculations. The experimental results of catalytic activity show that the addition of an appropriate amount of iron oxide has significant improvement for the NO conversion from 240 °C to 330 °C and the N2 selectivity from 150 °C to 330 °C. The XRD test also shows that the addition of iron oxide can greatly improve the dispersion of MnO2. In addition, DFT calculations indicate that the main process of N2 formation is the NH2NO decomposition and N-NO reaction. The N-NO reaction to form N2 is a unique reaction pathway possessed by MnFeOx/SiO2, which is the main reason for the high NO conversion and good N2 selectivity of MnFeOx/SiO2 catalyst and shows good synergy between manganese oxide and iron oxide.

The synergy between manganese oxide and iron oxide in NO catalytic removal with MnFeOx/SiO2 catalyst

Comparison of sulfur poisoning resistance of Ce/Mn doped γ-Fe2O3 (0 0 1) surface in NH3-SCR reaction with DFT method

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