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4 pages, 155 KiB

Open AccessEditorial

Selective Catalytic Reduction of NO_x

by Oliver Kröcher

Catalysts 2018, 8(10), 459; https://doi.org/10.3390/catal8100459 - 17 Oct 2018

Cited by 21 | Viewed by 3722

Abstract

n/a Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

Research

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9 pages, 2141 KiB

Open AccessArticle

Ammonia Concentration Distribution Measurements on Selective Catalytic Reduction Catalysts

by Rafal Sala, Jakub Dzida and Jaroslaw Krasowski

Catalysts 2018, 8(6), 231; https://doi.org/10.3390/catal8060231 - 1 Jun 2018

Cited by 10 | Viewed by 4370

Abstract

This work presents the methodology and accurate evaluation of ammonia concentration distribution measurements at the selective catalytic reduction (SCR) catalyst outlet cross-section. The uniformity of ammonia concentration is a crucial factor influencing overall SCR effectiveness, and it contributes to the necessity of employing [...] Read more.

This work presents the methodology and accurate evaluation of ammonia concentration distribution measurements at the selective catalytic reduction (SCR) catalyst outlet cross-section. The uniformity of ammonia concentration is a crucial factor influencing overall SCR effectiveness, and it contributes to the necessity of employing a reliable test method. The aftertreatment system design (mainly its geometrical features) can be evaluated in detail. The ammonia concentration is measured at the SCR catalyst outlet at grid points covering from the center to the outer edges of the catalyst. Its execution requires the introduction of a probe hovering over the back face of the SCR. To obtain the expected accuracy, it is necessary to measure a sufficient number of points in a reasonable timeframe. In order to achieve that, a fully automatic sampling device was developed. Sample results are presented showing the capabilities of the created test stand and its importance for the design development and validation stages of SCR-based engine aftertreatment. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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16 pages, 2193 KiB

Open AccessFeature PaperArticle

Nb-Modified Ce/Ti Oxide Catalyst for the Selective Catalytic Reduction of NO with NH₃ at Low Temperature

by Jawaher Mosrati, Hanan Atia, Reinhard Eckelt, Henrik Lund, Giovanni Agostini, Ursula Bentrup, Nils Rockstroh, Sonja Keller, Udo Armbruster and Mourad Mhamdi

Catalysts 2018, 8(5), 175; https://doi.org/10.3390/catal8050175 - 26 Apr 2018

Cited by 20 | Viewed by 5807

Abstract

Recently, great attention has been paid to Ceria-based materials for selective catalytic reduction (SCR) with NH₃ owing to their unique redox, oxygen storage, and acid-base properties. Two series of bimetallic catalysts issued from Titania modified by Ce and Nb were prepared by [...] Read more.

Recently, great attention has been paid to Ceria-based materials for selective catalytic reduction (SCR) with NH₃ owing to their unique redox, oxygen storage, and acid-base properties. Two series of bimetallic catalysts issued from Titania modified by Ce and Nb were prepared by the one-step sol-gel method (SG) and by the sol-gel route followed by impregnation (WI). The resulting core-shell and bulk catalysts were tested in NH₃-SCR of NO_x. The impregnated Nb5/Ce40/Ti100 (WI) catalyst displayed 95% NO_x conversion at 200 °C (GHSV = 60,000 mL·g⁻¹·h⁻¹, 1000 ppm NO_x, 1000 ppm NH₃, 5% O₂/He) without forming N₂O. The catalysts were characterized by various methods including ICP-OES, N₂-physisorption, XRD, Raman, NH₃-TPD, DRIFTS, XPS, and H₂-TPR. The results showed that the introduction of Nb decreases the surface area and strengthens the surface acidity. This behavior can be explained by the strong interaction between Ceria and Titania which generates Ce-O-Ti units, as well as a high concentration of amorphous or highly dispersed Niobia. This should be the reason for the excellent performance of the catalyst prepared by the sol-gel method followed by impregnation. Furthermore, Nb5/Ce40/Ti100 (WI) has the largest NH₃ adsorption capacity, which is helpful to promote the NH₃-SCR reaction. The long-term stability and the effect of H₂O on the catalysts were also evaluated. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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13 pages, 5206 KiB

Open AccessArticle

Mobility of NH₃-Solvated Cu^II Ions in Cu-SSZ-13 and Cu-ZSM-5 NH₃-SCR Catalysts: A Comparative Impedance Spectroscopy Study

by Valentina Rizzotto, Peirong Chen and Ulrich Simon

Catalysts 2018, 8(4), 162; https://doi.org/10.3390/catal8040162 - 18 Apr 2018

Cited by 24 | Viewed by 5733

Abstract

The mobility of NH₃-solvated Cu ions within the zeolite framework has been recently identified as a key factor for the kinetics of the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) over Cu-zeolite catalysts at low temperatures. [...] Read more.

The mobility of NH₃-solvated Cu ions within the zeolite framework has been recently identified as a key factor for the kinetics of the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) over Cu-zeolite catalysts at low temperatures. Here, we utilize in situ impedance spectroscopy to explore the mobility of NH₃-solvated Cu^II ions, i.e., Cu^II(NH₃)_n, in Cu-SSZ-13 and Cu-ZSM-5 zeolites with varied Cu ion exchange levels, and observed that both the zeolite framework (CHA or MFI) and the Cu exchange level influence the high-frequency dielectric relaxation processes that are associated with the short-range (local) motion of Cu^II(NH₃)_n. Our results suggest that the local motion of Cu^II(NH₃)_n species is favored within the CHA framework due to the unique cage structure, and thereby contribute to the overall ion conductivity at high frequencies, which, on the contrary, is not observed for ZSM-5, where NH₃-solvated Cu²⁺ ions do not experience a comparable constrained space for local motion. This study sheds new light on the mobility of Cu active sites under NH₃-SCR related reaction conditions and may contribute to an advanced understanding of the underlying mechanism. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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10 pages, 23788 KiB

Open AccessArticle

DRIFT Study on Promotion Effect of the Keggin Structure over V₂O₅-MoO₃/TiO₂ Catalysts for Low Temperature NH₃-SCR Reaction

by Rui Wu, Ningqiang Zhang, Lingcong Li, Hong He, Liyun Song and Wenge Qiu

Catalysts 2018, 8(4), 143; https://doi.org/10.3390/catal8040143 - 3 Apr 2018

Cited by 25 | Viewed by 5844

Abstract

Heteropoly acids (HPAs) with the Keggin structure have been widely used in NO_x removal. Two kinds of catalysts (those with and without the Keggin structure) are prepared for studying the effect of the Keggin structure on the NH₃-SCR reaction. A [...] Read more.

Heteropoly acids (HPAs) with the Keggin structure have been widely used in NO_x removal. Two kinds of catalysts (those with and without the Keggin structure) are prepared for studying the effect of the Keggin structure on the NH₃-SCR reaction. A series of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) analyses are conducted to investigate the surface-adsorbed species on the catalysts during the SCR reaction. The mechanism for enhancing low-temperature activity of the catalysts is proposed. Furthermore, the effect of NH₄⁺ in the Keggin structure is also investigated. Results indicate that both the Langmuir–Hinshelwood (L-H) and Eley–Rideal (E-R) mechanisms occurred in the NH₃-SCR reaction over the catalyst with the Keggin structure (Cat-A); in addition, when more acid sites are provided, NO_x species activity is improved and more NH₄⁺ ions participate in reaction over Cat-A, thus promoting SCR activity. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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17 pages, 6295 KiB

Open AccessArticle

The Role of Fe₂O₃ Species in Depressing the Formation of N₂O in the Selective Reduction of NO by NH₃ over V₂O₅/TiO₂-Based Catalysts

by Moon Hyeon Kim and Ki Hyuck Yang

Catalysts 2018, 8(4), 134; https://doi.org/10.3390/catal8040134 - 30 Mar 2018

Cited by 15 | Viewed by 5677

Abstract

Promotion of 2.73% Fe₂O₃ in an in-house-made V₂O₅-WO₃/TiO₂ (VWT) and a commercial V₂O₅-WO₃/TiO₂ (c-VWT) has been investigated as a cost effective approach to the suppression of [...] Read more.

Promotion of 2.73% Fe₂O₃ in an in-house-made V₂O₅-WO₃/TiO₂ (VWT) and a commercial V₂O₅-WO₃/TiO₂ (c-VWT) has been investigated as a cost effective approach to the suppression of N₂O formation in the selective catalytic reduction of NO by NH₃ (NH₃-SCR). The promoted VWT and c-VWT catalysts all gave a significantly decreased N₂O production at temperatures >400 °C compared to the unpromoted samples. However, such a promotion led to the loss in high temperature NO conversion, mainly due to the oxidation of NH₃ to N-containing gases, particularly NO. Characterization of the unpromoted and promoted catalysts using X-ray diffraction (XRD), NH₃ adsorption-desorption, and Raman spectroscopy techniques could explain the reason why the promotion showed much lower N₂O formation levels at high temperatures. The addition of Fe₂O₃ to c-VWT resulted in redispersion of the V₂O₅ species, although this was not visible for 2.73% Fe₂O₃/VWT. The iron oxides exist as a highly-dispersed noncrystalline α-Fe₂O₃ in the promoted catalysts. These Raman spectra had a new Raman signal that could be tentatively assigned to Fe₂O₃-induced tetrahedrally coordinated polymeric vanadates and/or surface V-O-Fe species with significant electronic interactions between the both metal oxides. Calculations of the monolayer coverage of each metal oxide and the surface total coverage are reasonably consistent with Raman measurements. The proposed vanadia-based surface polymeric entities may play a key role for the substantial reduction of N₂O formed at high temperatures by NH₃ species adsorbed strongly on the promoted catalysts. This reaction is a main pathway to greatly suppress the extent of N₂O formation in NH₃-SCR reaction over the promoted catalysts. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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13 pages, 25203 KiB

Open AccessEditor’s ChoiceArticle

Investigation of Iron Vanadates for Simultaneous Carbon Soot Abatement and NH₃-SCR

by Marzia Casanova, Sara Colussi and Alessandro Trovarelli

Catalysts 2018, 8(4), 130; https://doi.org/10.3390/catal8040130 - 26 Mar 2018

Cited by 9 | Viewed by 4652

Abstract

FeVO₄ and Fe_0.5Er_0.5VO₄ were prepared and loaded over standard Selective Catalytic Reduction (SCR) supports based on TiO₂-WO₃-SiO₂ (TWS) and redox active supports like CeO₂ and CeZrO₂ with the aim of [...] Read more.

FeVO₄ and Fe_0.5Er_0.5VO₄ were prepared and loaded over standard Selective Catalytic Reduction (SCR) supports based on TiO₂-WO₃-SiO₂ (TWS) and redox active supports like CeO₂ and CeZrO₂ with the aim of finding a suitable formulation for simultaneous soot abatement and NH₃-SCR and to understand the level of interaction between the two reactions. A suitable bi-functional material was identified in the composition FeVO₄/CeZrO₂ where an SCR active component is added over a redox active support, to increase carbon oxidation properties. The influence of the presence of ammonia in soot oxidation and the effect of the presence of soot on SCR reaction have been addressed. It is found that the addition of NO and NO/NH₃ mixtures decreases at different levels the oxidation temperature of carbon soot, while the presence of carbon adversely affects the NH₃-SCR reaction by increasing the oxidation of NH₃ to NO, thus lowering the NO removal efficiency. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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15 pages, 4497 KiB

Open AccessArticle

Enhanced Low Temperature NO Reduction Performance via MnO_x-Fe₂O₃/Vermiculite Monolithic Honeycomb Catalysts

by Ke Zhang, Feng Yu, Mingyuan Zhu, Jianming Dan, Xugen Wang, Jinli Zhang and Bin Dai

Catalysts 2018, 8(3), 100; https://doi.org/10.3390/catal8030100 - 28 Feb 2018

Cited by 47 | Viewed by 6746

Abstract

Selective catalytic reduction of NO_x by ammonia (NH₃-SCR) was the most efficient and economic technology for De-NO_x applications. Therefore, a series of MnO_x/vermiculite (VMT) and MnO_x-Fe₂O₃/VMT catalysts were prepared by an [...] Read more.

Selective catalytic reduction of NO_x by ammonia (NH₃-SCR) was the most efficient and economic technology for De-NO_x applications. Therefore, a series of MnO_x/vermiculite (VMT) and MnO_x-Fe₂O₃/VMT catalysts were prepared by an impregnation method for the selective catalytic reduction (SCR) of nitrogen oxides (NO_x). The MnO_x-Fe₂O₃/VMT catalysts provided an excellent NO conversion of 96.5% at 200 °C with a gas hourly space velocity (GHSV) of 30,000 h⁻¹ and an NO concentration of 500 ppm. X-ray photoelectron spectroscopy results indicated that the Mn and Fe oxides of the MnO_x-Fe₂O₃/VMT catalyst were mainly composed of MnO₂ and Fe₂O₃. However, the MnO₂ and Fe₂O₃ components were well dispersed because no discernible MnO₂ and Fe₂O₃ phases were observed in X-ray powder diffraction spectra. Corresponding MnO_x-Fe₂O₃/VMT monolithic honeycomb catalysts (MHCs) were prepared by an extrusion method, and the MHCs achieved excellent SCR activity at low temperature, with an NO conversion greater than 98.6% at 150 °C and a GHSV of 4000 h⁻¹. In particular, the MnO_x-Fe₂O₃/VMT MHCs provided a good SCR activity at room temperature (20 °C), with an NO conversion of 62.2% (GHSV = 1000 h⁻¹). In addition, the NO reduction performance of the MnO_x-Fe₂O₃/VMT MHCs also demonstrated an excellent SO₂ resistance. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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14 pages, 3032 KiB

Open AccessArticle

Mn-Ce-V-WO_x/TiO₂ SCR Catalysts: Catalytic Activity, Stability and Interaction among Catalytic Oxides

by Xuteng Zhao, Lei Mao and Guojun Dong

Catalysts 2018, 8(2), 76; https://doi.org/10.3390/catal8020076 - 12 Feb 2018

Cited by 26 | Viewed by 5715

Abstract

A series of Mn-Ce-V-WO_x/TiO₂ composite oxide catalysts with different molar ratios (active components/TiO₂ = 0.1, 0.2, 0.3, 0.6) have been prepared by wet impregnation method and tested in selective catalytic reduction (SCR) of NO by NH₃ in a [...] Read more.

A series of Mn-Ce-V-WO_x/TiO₂ composite oxide catalysts with different molar ratios (active components/TiO₂ = 0.1, 0.2, 0.3, 0.6) have been prepared by wet impregnation method and tested in selective catalytic reduction (SCR) of NO by NH₃ in a wide temperature range. These catalysts were also characterized by X-ray diffraction (XRD), Transmission Electron Microscope (TEM), in situ Fourier Transform infrared spectroscopy (in situ FTIR), H₂-Temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS). The results show the catalyst with a molar ratio of active components/TiO₂ = 0.2 exhibits highest NO conversion value between 150 °C to 400 °C and good resistance to H₂O and SO₂ at 250 °C with a gas hourly space velocity (GHSV) value of 40,000 h⁻¹. Different oxides are well dispersed and interact with each other. NH₃ and NO are strongly adsorbed on the catalyst surface and the adsorption of the reactant gas leads to a redox cycle with the valence state change among the surface oxides. The adsorption of SO₂ on Mn⁴⁺ and Ce⁴⁺ results in good H₂O and SO₂ resistance of the catalyst, but the effect of Mn and Ce are more than superior water and sulfur resistance. The diversity of valence states of the four active components and their high oxidation-reduction performance are the main reasons for the high NO conversion in this system. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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14 pages, 2283 KiB

Open AccessArticle

Surface Species and Metal Oxidation State during H₂-Assisted NH₃-SCR of NO_x over Alumina-Supported Silver and Indium

by Linda Ström, Per-Anders Carlsson, Magnus Skoglundh and Hanna Härelind

Catalysts 2018, 8(1), 38; https://doi.org/10.3390/catal8010038 - 19 Jan 2018

Cited by 19 | Viewed by 5310

Abstract

Alumina-supported silver and indium catalysts are investigated for the hydrogen-assisted selective catalytic reduction (SCR) of NO_x with ammonia. Particularly, we focus on the active phase of the catalyst and the formation of surface species, as a function of the gas environment. Diffuse [...] Read more.

Alumina-supported silver and indium catalysts are investigated for the hydrogen-assisted selective catalytic reduction (SCR) of NO_x with ammonia. Particularly, we focus on the active phase of the catalyst and the formation of surface species, as a function of the gas environment. Diffuse reflectance ultraviolet-visible (UV-vis) spectroscopy was used to follow the oxidation state of the silver and indium phases, and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to elucidate the formation of surface species during SCR conditions. In addition, the NO_x reduction efficiency of the materials was evaluated using H₂-assisted NH₃-SCR. The DRIFTS results show that the Ag/Al₂O₃ sample forms NO-containing surface species during SCR conditions to a higher extent compared to the In/Al₂O₃ sample. The silver sample also appears to be more reduced by H₂ than the indium sample, as revealed by UV-vis spectroscopic experiments. Addition of H₂, however, may promote the formation of highly dispersed In₂O₃ clusters, which previously have been suggested to be important for the SCR reaction. The affinity to adsorb NH₃ is confirmed by both temperature programmed desorption (NH₃-TPD) and in situ DRIFTS to be higher for the In/Al₂O₃ sample compared to Ag/Al₂O₃. The strong adsorption of NH₃ may inhibit (self-poison) the NH₃ activation, thereby hindering further reaction over this catalyst, which is also shown by the lower SCR activity compared to Ag/Al₂O₃. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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16 pages, 2756 KiB

Open AccessArticle

Preparation and Performance of Modified Red Mud-Based Catalysts for Selective Catalytic Reduction of NO_x with NH₃

by Jingkun Wu, Zhiqiang Gong, Chunmei Lu, Shengli Niu, Kai Ding, Liting Xu and Kang Zhang

Catalysts 2018, 8(1), 35; https://doi.org/10.3390/catal8010035 - 19 Jan 2018

Cited by 42 | Viewed by 5908

Abstract

Bayer red mud was selected, and the NH₃-SCR activity was tested in a fixed bed in which the typical flue gas atmosphere was simulated. Combined with XRF, XRD, BET, SEM, TG and NH₃-Temperature Programmed Desorption (TPD) characterization, the denitration [...] Read more.

Bayer red mud was selected, and the NH₃-SCR activity was tested in a fixed bed in which the typical flue gas atmosphere was simulated. Combined with XRF, XRD, BET, SEM, TG and NH₃-Temperature Programmed Desorption (TPD) characterization, the denitration characteristics of Ce-doped red mud catalysts were studied on the basis of alkali-removed red mud. The results showed that typical red mud was a feasible material for denitration catalyst. Acid washing and calcining comprised the best treatment process for raw red mud, which reduced the content of alkaline substances, cleared the catalyst pore and optimized the particle morphology with dispersion. In the temperature range of 300–400 °C, the denitrification efficiency of calcined acid washing of red mud catalyst (ARM) was more than 70%. The doping of Ce significantly enhanced NH₃ adsorption from weak, medium and strong acid sites, reduced the crystallinity of α-Fe₂O₃ in ARM, optimized the specific surface area and broadened the active temperature window, which increased the NO_x conversion rate by an average of nearly 20% points from 250–350 °C. The denitration efficiency of Ce_0.3/ARM at 300 °C was as high as 88%. The optimum conditions for the denitration reaction of the Ce_0.3/ARM catalyst were controlled as follows: Gas Hourly Space Velocity (GHSV) of 30,000 h⁻¹, O₂ volume fraction of 3.5–4% and the NH₃/NO molar ratio ([NH₃/NO]) of 1.0. The presence of SO₂ in the feed had an irreversible negative effect on the activity of the Ce_0.3/ARM catalyst. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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7635 KiB

Open AccessArticle

Influence of the Sodium Impregnation Solvent on the Deactivation of Cu/FER-Exchanged Zeolites Dedicated to the SCR of NO_x with NH₃

by Marie-Laure Tarot, Mathias Barreau, Daniel Duprez, Vincent Lauga, Eduard Emil Iojoiu, Xavier Courtois and Fabien Can

Catalysts 2018, 8(1), 3; https://doi.org/10.3390/catal8010003 - 23 Dec 2017

Cited by 10 | Viewed by 5373

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 [...] Read more.

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 NO_x conversion at low temperature (250 °C) appeared mainly affected by the loss in NH₃ adsorption capacity whereas the deNO_x 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 NO_x)

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4450 KiB

Open AccessArticle

Consideration of the Role of Plasma in a Plasma-Coupled Selective Catalytic Reduction of Nitrogen Oxides with a Hydrocarbon Reducing Agent

by Byeong Ju Lee, Ho-Chul Kang, Jin Oh Jo and Young Sun Mok

Catalysts 2017, 7(11), 325; https://doi.org/10.3390/catal7110325 - 31 Oct 2017

Cited by 13 | Viewed by 5318

Abstract

The purpose of this study is to explain how plasma improves the performance of selective catalytic reduction (SCR) of nitrogen oxides (NO_x) with a hydrocarbon reducing agent. In the plasma-coupled SCR process, NO_x reduction was performed with n-heptane as a [...] Read more.

The purpose of this study is to explain how plasma improves the performance of selective catalytic reduction (SCR) of nitrogen oxides (NO_x) with a hydrocarbon reducing agent. In the plasma-coupled SCR process, NO_x 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 NO_x 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 NO_x 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 NO_x 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 NO_x removal efficiency with the aldehyde reducing agent was higher as the number of carbons in the aldehyde was more; for example, the NO_x 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 NO_x)

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2148 KiB

Open AccessArticle

Concept of Vaporized Urea Dosing in Selective Catalytic Reduction

by Rafal Sala, Piotr Bielaczyc and Marek Brzezanski

Catalysts 2017, 7(10), 307; https://doi.org/10.3390/catal7100307 - 19 Oct 2017

Cited by 12 | Viewed by 8108

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 NO_x conversion efficiency in the catalyst. It can [...] Read more.

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 NO_x 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 NO_x 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 NO_x)

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2189 KiB

Open AccessArticle

Experimental Research of an Active Solution for Modeling In Situ Activating Selective Catalytic Reduction Catalyst

by Tuo Ye, Donglin Chen, Yanshan Yin, Jing Liu and Xi Zeng

Catalysts 2017, 7(9), 258; https://doi.org/10.3390/catal7090258 - 31 Aug 2017

Cited by 10 | Viewed by 5571

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 [...] Read more.

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 NO_x)

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Review

Jump to: Editorial, Research

23 pages, 36332 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Progress in Atomic-Level Understanding of Cu/SSZ-13 Selective Catalytic Reduction Catalysts

by Feng Gao and Charles H. F. Peden

Catalysts 2018, 8(4), 140; https://doi.org/10.3390/catal8040140 - 31 Mar 2018

Cited by 105 | Viewed by 9620

Abstract

Cu/SSZ-13 Selective Catalytic Reduction (SCR) catalysts have been extensively studied for the past five-plus years. New and exciting fundamental and applied science has appeared in the literature quite frequently over this time. In this short review, a few topics specifically focused on a [...] Read more.

Cu/SSZ-13 Selective Catalytic Reduction (SCR) catalysts have been extensively studied for the past five-plus years. New and exciting fundamental and applied science has appeared in the literature quite frequently over this time. In this short review, a few topics specifically focused on a molecular-level understanding of this catalyst are summarized: (1) The nature of the active sites and, in particular, their transformations under varying reaction conditions that include dehydration, the presence of the various SCR reactants and hydrothermal aging; (2) Discussions of standard and fast SCR reaction mechanisms. Considerable progress has been made, especially in the last couple of years, on standard SCR mechanisms. In contrast, mechanisms for fast SCR are much less understood. Possible reaction paths are hypothesized for this latter case to stimulate further investigations; (3) Discussions of rational catalyst design based on new knowledge obtained regarding catalyst stability, overall catalytic performance and mechanistic catalytic chemistry. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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11 pages, 805 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Strategies of Coping with Deactivation of NH₃-SCR Catalysts Due to Biomass Firing

by Leonhard Schill and Rasmus Fehrmann

Catalysts 2018, 8(4), 135; https://doi.org/10.3390/catal8040135 - 30 Mar 2018

Cited by 11 | Viewed by 4940

Abstract

Firing of biomass can lead to rapid deactivation of the vanadia-based NH₃-SCR catalyst, which reduces NO_x to harmless N₂. The deactivation is mostly due to the high potassium content in biomasses, which results in submicron aerosols containing mostly [...] Read more.

Firing of biomass can lead to rapid deactivation of the vanadia-based NH₃-SCR catalyst, which reduces NO_x to harmless N₂. The deactivation is mostly due to the high potassium content in biomasses, which results in submicron aerosols containing mostly KCl and K₂SO₄. The main mode of deactivation is neutralization of the catalyst’s acid sites. Four ways of dealing with high potassium contents were identified: (1) potassium removal by adsorption, (2) tail-end placement of the SCR unit, (3) coating SCR monoliths with a protective layer, and (4) intrinsically potassium tolerant catalysts. Addition of alumino silicates, often in the form of coal fly ash, is an industrially proven method of removing K aerosols from flue gases. Tail-end placement of the SCR unit was also reported to result in acceptable catalyst stability; however, flue-gas reheating after the flue gas desulfurization is, at present, unavoidable due to the lack of sulfur and water tolerant low temperature catalysts. Coating the shaped catalysts with thin layers of, e.g., MgO or sepiolite reduces the K uptake by hindering the diffusion of K⁺ into the catalyst pore system. Intrinsically potassium tolerant catalysts typically contain a high number of acid sites. This can be achieved by, e.g., using zeolites as support, replacing WO₃ with heteropoly acids, and by preparing highly loaded, high surface area, very active V₂O₅/TiO₂ catalyst using a special sol-gel method. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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Open AccessReview

Sulfur and Water Resistance of Mn-Based Catalysts for Low-Temperature Selective Catalytic Reduction of NOx: A Review

by Chen Gao, Jian-Wen Shi, Zhaoyang Fan, Ge Gao and Chunming Niu

Catalysts 2018, 8(1), 11; https://doi.org/10.3390/catal8010011 - 7 Jan 2018

Cited by 100 | Viewed by 8674

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-NO_x 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-NO_x 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 NO_x. Firstly, the poison mechanisms of H₂O and SO₂ are introduced in detail, respectively. Secondly, Mn-based catalysts are divided into three categories—single MnO_x 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 NO_x are proposed. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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