Special Issue "Selective Catalytic Reduction of NOx"

A special issue of Catalysts (ISSN 2073-4344).

Deadline for manuscript submissions: 28 February 2018

Special Issue Editor

Guest Editor
Prof. Dr. Oliver Kröcher

Paul Scherrer Institut, CH-5232 Villigen, Switzerland
Website | E-Mail
Interests: emission control catalysts, selective catalytic reduction, diesel oxidation catalysts, methane oxidation, bioenergy, catalytic processes for gaseous and liquid biofuels, operando spectroscopy

Special Issue Information

Dear Colleagues,

The recent diesel scandal made the public again aware of the fact that NOx emissions from diesel engines are a major threat to human health and by no means easy to avoid. The most efficient process to reduce NOx emissions from lean exhaust gases is selective catalytic reduction (SCR) with ammonia, which has undergone tremendous development over the past decades. Originally only applied in stationary power plants and industrial installations, SCR systems are now installed also in millions of mobile diesel engines, ranging from off-road machineries, heavy-duty and light-duty trucks and passenger cars, to locomotives and ships. These applications are particularly challenging due to the varying operation conditions of mobile diesel engines with respect to exhaust gas temperature, exhaust gas flow, NOx inlet concentrations, ambient temperature and available installation space. As a matter of fact, many problems are still encountered with all the different SCR applications and much research is being conducted to overcome them.

Submissions to this special issue on “Selective Catalytic Reduction of NOx” are welcome in the form of original research papers or short reviews that reflect the state of research in the SCR field on the following topics: Selective catalytic reduction of NOx (SCR) for diesel vehicles/stationary power plants/industrial installations, SCR catalyst research and development (V-based catalysts, Fe-zeolites, Cu-zeolites), catalyst deactivation, SCR reaction mechanisms, SCR kinetics and modelling, structure-function relationships in SCR catalysts and dosage/decomposition of reducing agents for SCR.

Prof. Dr. Oliver Kröcher
Guest Editor

Manuscript Submission Information

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Keywords

  • Selective catalytic reduction (SCR) with ammonia/urea
  • SCR in diesel vehicles, stationary power plants and industrial installations
  • SCR catalyst research and development on V-based systems, Fe-zeolites and Cu-zeolites
  • Catalyst deactivation
  • SCR reaction mechanisms
  • SCR kinetics and modelling
  • Structure-function relationships in SCR catalysts
  • Control, dosage and decomposition of reducing agents for SCR

Published Papers (5 papers)

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Research

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Open AccessArticle Influence of the Sodium Impregnation Solvent on the Deactivation of Cu/FER-Exchanged Zeolites Dedicated to the SCR of NOx with NH3
Catalysts 2018, 8(1), 3; doi:10.3390/catal8010003
Received: 24 November 2017 / Revised: 18 December 2017 / Accepted: 19 December 2017 / Published: 23 December 2017
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Abstract
The effect of the sodium addition mode was investigated on model Cu/FER selective catalytic reduction (SCR) catalysts with two copper loadings (2.8 wt. % and 6.1 wt. %) in order to compare samples with or without over-exchanged copper. Na was added by wet-impregnation
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The effect of the sodium addition mode was investigated on model Cu/FER selective catalytic reduction (SCR) catalysts with two copper loadings (2.8 wt. % and 6.1 wt. %) in order to compare samples with or without over-exchanged copper. Na was added by wet-impregnation using two solvents: water or ethanol. Catalysts were evaluated in Standard and Fast-SCR conditions, as well as in NO and NH3 oxidation. They were characterized by H2-TPR, NO and NH3 adsorption monitored by FT-IR. As expected, whatever the copper loading, ammonia adsorption capacity was decreased by Na additions. Interestingly, characterizations also showed that Na impregnation in water favors the migration of the Cu-exchanged species, leading to the formation of CuO extra-framework compounds. Consequently, for both copper loadings, Na impregnation in water led to a stronger catalyst deactivation than impregnation in ethanol. Finally, the NOx conversion at low temperature (250 °C) appeared mainly affected by the loss in NH3 adsorption capacity whereas the deNOx deactivation at high temperature (500 °C) was rather governed by the decrease in the exchanged copper ratio, which also induced a partial inhibition of NO and NH3 oxidation behaviors. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx)
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Open AccessArticle Consideration of the Role of Plasma in a Plasma-Coupled Selective Catalytic Reduction of Nitrogen Oxides with a Hydrocarbon Reducing Agent
Catalysts 2017, 7(11), 325; doi:10.3390/catal7110325
Received: 13 October 2017 / Revised: 26 October 2017 / Accepted: 28 October 2017 / Published: 31 October 2017
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Abstract
The purpose of this study is to explain how plasma improves the performance of selective catalytic reduction (SCR) of nitrogen oxides (NOx) with a hydrocarbon reducing agent. In the plasma-coupled SCR process, NOx reduction was performed with n-heptane as a
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The purpose of this study is to explain how plasma improves the performance of selective catalytic reduction (SCR) of nitrogen oxides (NOx) with a hydrocarbon reducing agent. In the plasma-coupled SCR process, NOx reduction was performed with n-heptane as a reducing agent over Ag/γ-Al2O3 as a catalyst. We found that the plasma decomposes n-heptane into several oxygen-containing products such as acetaldehyde, propionaldehyde and butyraldehyde, which are more reactive than the parent molecule n-heptane in the SCR process. Separate sets of experiments using acetaldehyde, propionaldehyde and butyraldehyde, one by one, as a reductant in the absence of plasma, have clearly shown that the presence of these partially oxidized compounds greatly enhanced the NOx conversion. The higher the discharge voltage, the more the amounts of such partially oxidized products. The oxidative species produced by the plasma easily converted NO into NO2, but the increase of the NO2 fraction was found to decrease the NOx conversion. Consequently, it can be concluded that the main role of plasma in the SCR process is to produce partially oxidized compounds (aldehydes), having better reducing power. The catalyst-alone NOx removal efficiency with n-heptane at 250 °C was measured to be less than 8%, but it increased to 99% in the presence of acetaldehyde at the same temperature. The NOx removal efficiency with the aldehyde reducing agent was higher as the number of carbons in the aldehyde was more; for example, the NOx removal efficiencies at 200 °C with butyraldehyde, propionaldehyde and acetaldehyde were measured to be 83.5%, 58.0% and 61.5%, respectively, which were far above the value (3%) obtained with n-heptane. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx)
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Open AccessArticle Concept of Vaporized Urea Dosing in Selective Catalytic Reduction
Catalysts 2017, 7(10), 307; doi:10.3390/catal7100307
Received: 7 September 2017 / Revised: 28 September 2017 / Accepted: 13 October 2017 / Published: 19 October 2017
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Abstract
This work tried to identify the influence of dosing vaporized urea solution in a selective catalytic reduction (SCR) system. In the SCR method, optimising the urea evaporation and mixing properties can significantly improve the NOx conversion efficiency in the catalyst. It can
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This work tried to identify the influence of dosing vaporized urea solution in a selective catalytic reduction (SCR) system. In the SCR method, optimising the urea evaporation and mixing properties can significantly improve the NOx conversion efficiency in the catalyst. It can also exert a positive effect on the uniformity of NH3 concentration distribution across the catalyst face. The concept of an electrically evaporated urea-dosing system was investigated and it was found that urea pre-heating prior to introduction into the exhaust gas is favourable for enhancing NOx removal under steady-state and transient engine operation. In the urea evaporating system the heating chamber was of a cylindrical tube shape and the urea vapour was introduced into the exhaust by means of a Venturi orifice. The concept urea dosing was only a custom-made solution, but proved to be superior to the regular dosing system operating in the liquid phase. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx)
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Open AccessArticle Experimental Research of an Active Solution for Modeling In Situ Activating Selective Catalytic Reduction Catalyst
Catalysts 2017, 7(9), 258; doi:10.3390/catal7090258
Received: 21 July 2017 / Revised: 29 August 2017 / Accepted: 29 August 2017 / Published: 31 August 2017
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Abstract
The effect of active solutions suitable for the in situ activation of selective catalytic reduction (SCR) catalysts was experimentally investigated using a designed in situ activation modeling device. To gain further insight, scanning electron microscopy (SEM), specific surface area analysis (BET), Fourier transform
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The effect of active solutions suitable for the in situ activation of selective catalytic reduction (SCR) catalysts was experimentally investigated using a designed in situ activation modeling device. To gain further insight, scanning electron microscopy (SEM), specific surface area analysis (BET), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS) analyses were used to investigate the effects of different reaction conditions on the characteristics of the deactivated catalysts. The activation effect of loading V2O5, WO3 and MoO3 on the surface of the deactivated catalysts was analyzed and the correlation to the denitrification activity was determined. The results demonstrate that the prepared activating solution of 1 wt % vanadium (V), 9 wt % tungsten (W), and 6 wt % molybdenum (Mo) has a beneficial effect on the deactivation of the catalyst. The activated catalyst resulted in a higher NO removal rate when compared to the deactivated catalyst. Furthermore, the NO removal rate of the activated catalyst reached a maximum of 32%. The activity of the SCR catalyst is closely linked to the concentration of the active ingredients. When added in optimum amounts, the active ingredients helped to restore the catalytic activity. In particular, the addition of active ingredients, the availability of labile surface oxygen, and the presence of small pores improved the denitrification efficiency. Based on these results, active solutions can effectively solve the problem of denitrification catalyst deactivation. These findings are a reference for the in-situ activation of the selective catalytic reduction of nitrogen oxides (SCR-DeNOx) catalyst. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx)
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Review

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Open AccessReview Sulfur and Water Resistance of Mn-Based Catalysts for Low-Temperature Selective Catalytic Reduction of NOx: A Review
Catalysts 2018, 8(1), 11; doi:10.3390/catal8010011
Received: 6 December 2017 / Revised: 26 December 2017 / Accepted: 3 January 2018 / Published: 7 January 2018
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Abstract
Selective catalytic reduction (SCR) with NH3 is the most efficient and economic flue gas denitrification technology developed to date. Due to its high low-temperature catalytic activity, Mn-based catalysts present a great prospect for application in SCR de-NOx at low temperatures. However,
[...] Read more.
Selective catalytic reduction (SCR) with NH3 is the most efficient and economic flue gas denitrification technology developed to date. Due to its high low-temperature catalytic activity, Mn-based catalysts present a great prospect for application in SCR de-NOx at low temperatures. However, overcoming the poor resistance of Mn-based catalysts to H2O and SO2 poison is still a challenge. This paper reviews the recent progress on the H2O and SO2 resistance of Mn-based catalysts for the low-temperature SCR of NOx. Firstly, the poison mechanisms of H2O and SO2 are introduced in detail, respectively. Secondly, Mn-based catalysts are divided into three categories—single MnOx catalysts, Mn-based multi-metal oxide catalysts, and Mn-based supported catalysts—to review the research progress of Mn-based catalysts for H2O and SO2 resistance. Thirdly, several strategies to reduce the poisonous effects of H2O and SO2, such as metal modification, proper support, the combination of metal modification and support, the rational design of structure and morphology, are summarized. Finally, perspectives and future directions of Mn-based catalysts for the low-temperature SCR of NOx are proposed. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx)
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