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Selective Catalytic Reduction of NOx by NH3
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Selective Catalytic Reduction of NOx by NH3

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

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 32277

Special Issue Editors

Prof. Dr. Fabio Alessandro Deorsola

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Guest Editor
Politecnico di Torino, Dept Sci Appl & Technol, Corso Duca Abruzzi 24, I-10129 Turin, Italy
Interests: heterogeneous catalysis for environment and energy; NOx abatement; soot abatement; power-to-gas; aqueous phase reforming; CO2 valorization; water splitting
Prof. Dr. Lidia Castoldi

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Guest Editor
Politecnico di Milano – Dip. Energia – via privata La Masa 34 – 20156 Milano, Italy
Interests: heterogeneous catalysis for environment and energy; NOx abatement; soot abatement; CO2 valorization

Special Issue Information

Dear Colleagues,

Nitrogen oxides (NOx) still represent one of the most dangerous pollutants for human health, with more than 70,000 premature deaths attributed to them each year in Europe. Their key role has been widely recognized in both the eutrophication and acidification of ecosystems and in photochemical smog and tropospheric ozone formation. They are produced during high-temperature combustion processes and road transport accounts for almost 40% of their emissions, followed by energy production, distribution and industrial use, and the commercial, institutional, and household sectors. Among the different techniques investigated, ammonia-mediated selective catalytic reduction (SCR) represents the best option for achieving maximum NOx abatement efficiency. Although several advancements have been observed in the last years in this technology and the NOx concentrations and exposures have continued to decrease, they are still above the limit values and much research effort is needed to overcome the issues challenging the exploitation of SCR in different applications, both stationary and dynamics. This Special Issue intends to collect the most recent progress in the NH3-SCR technique, from the development of new catalysts to the study of the mechanisms, as well as poisoning phenomena up to its application, especially in synergy with other pollutants abatement techniques (LNT, SCR, etc.).

Prof. Dr. Fabio Alessandro Deorsola
Prof. Dr. Lidia Castoldi
Guest Editors

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Keywords

  • NH3-SCR catalysts
  • SCR reaction mechanism and kinetics
  • Catalyst poisoning
  • Low-T NH3-SCR
  • Ammonia/urea dosing
  • SCRoF
  • SCR-LNT
  • Transition metals
  • Zeolites

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Related Special Issue

Published Papers (6 papers)

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Research

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17 pages, 4082 KiB  
Article
MnOx Supported on Hierarchical SAPO-34 for the Low-Temperature Selective Catalytic Reduction of NO with NH3: Catalytic Activity and SO2 Resistance
by Lusha Zhou, Jinkun Guan, Chenglong Yu and Bichun Huang
Catalysts 2021, 11(3), 314; https://doi.org/10.3390/catal11030314 - 27 Feb 2021
Cited by 13 | Viewed by 2710
Abstract
The ethanol dispersion method was employed to synthesize a series of MnOx/SAPO-34 catalysts using SAPO-34 with the hierarchical pore structure as the zeolite carrier, which were prepared by facile acid treatment with citric acid. Physicochemical properties of catalysts were characterized by [...] Read more.
The ethanol dispersion method was employed to synthesize a series of MnOx/SAPO-34 catalysts using SAPO-34 with the hierarchical pore structure as the zeolite carrier, which were prepared by facile acid treatment with citric acid. Physicochemical properties of catalysts were characterized by XRD, XPS, BET, TEM, NH3-TPD, SEM, FT-IR, Py-IR, H2-TRP and TG/DTG. NH3-SCR performances of the hierarchical MnOx/SAPO-34 catalysts were evaluated at low temperatures. Results show that citric acid etching solution at a concentration of 0.1 mol/L yielded a hierarchical MnOx/SAPO-34-0.1 catalyst with ca.15 wt.% Mn loading, exhibiting optimal catalytic activity and SO2 tolerance at low temperatures. Almost 100% NO conversion and over 90% N2 selectivity at 120 °C under a gas hourly space velocity (GHSV) of 40,000 h−1 could be obtained over this sample. Furthermore, the NO conversion was still higher than 65% when 100 ppm SO2 was introduced to the reaction gas for 4 h. These could be primarily attributed to the large specific surface area, high surface acidity concentration and abundant chemisorbed oxygen species provided by the hierarchical pore structure, which could also increase the mass transfer of the reaction gas. This finding suggests that the NH3-SCR activity and SO2 poisoning tolerance of hierarchical MnOx/SAPO-34 catalysts at low temperatures can be improved by controlling the morphology of the catalysts, which might supply a rational strategy for the design and synthesis of Mn-based SCR catalysts. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx by NH3)
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14 pages, 2896 KiB  
Article
Iron-Based Composite Oxide Catalysts Tuned by CTAB Exhibit Superior NH3–SCR Performance
by Wenshuo Zhang, Xiaoyan Shi, Meng Gao, Jingjing Liu, Zhihui Lv, Yingjie Wang, Yanlong Huo, Chang Cui, Yunbo Yu and Hong He
Catalysts 2021, 11(2), 224; https://doi.org/10.3390/catal11020224 - 8 Feb 2021
Cited by 10 | Viewed by 2813
Abstract
Iron-based oxide catalysts for the NH3–SCR (selective catalytic reduction of NOx by NH3) reaction have gained attention due to their high catalytic activity and structural adjustability. In this work, iron–niobium, iron–titanate and iron–molybdenum composite oxides were synthesized by [...] Read more.
Iron-based oxide catalysts for the NH3–SCR (selective catalytic reduction of NOx by NH3) reaction have gained attention due to their high catalytic activity and structural adjustability. In this work, iron–niobium, iron–titanate and iron–molybdenum composite oxides were synthesized by a co-precipitation method with or without the assistance of hexadecyl trimethyl ammonium bromide (CTAB). The catalysts synthesized with the assistance of CTAB (FeM0.3Ox-C, M = Nb, Ti, Mo) showed superior SCR performance in an operating temperature range from 150 °C to 400 °C compared to those without CTAB addition (FeM0.3Ox, M = Nb, Ti, Mo). To reveal such enhancement, the catalysts were characterized by N2-physisorption, XRD (Powder X-ray diffraction), NH3-TPD (temperature-programmed desorption of ammonia), DRIFTS (Diffuse Reflectance Infrared Fourier Transform Spectroscopy), XPS (X-ray Photoelectron Spectroscopy), and H2-TPR (H2-Total Physical Response). It was found that the crystalline phase of Fe2O3 formed was influenced by the presence of CTAB in the preparation process, which favored the formation of crystalline γ-Fe2O3. Owing to the changed structure, the redox-acid properties of FeM0.3Ox-C catalysts were modified, with higher exposure of acid sites and improved ability of NO oxidation to NO2 at low-temperature, both of which also contributed to the improvement of NOx conversion. In addition, the weakened redox ability of Fe prevented the over-oxidation of NH3, thus accounting for the greatly improved high-temperature activity as well as N2 selectivity. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx by NH3)
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15 pages, 3679 KiB  
Article
Novel Preparation of Cu and Fe Zirconia Supported Catalysts for Selective Catalytic Reduction of NO with NH3
by Katarzyna Świrk, Ye Wang, Changwei Hu, Li Li, Patrick Da Costa and Gérard Delahay
Catalysts 2021, 11(1), 55; https://doi.org/10.3390/catal11010055 - 2 Jan 2021
Cited by 9 | Viewed by 2802
Abstract
Copper and iron promoted ZrO2 catalysts were prepared by one-pot synthesis using urea. The studied catalysts were characterized by XRD, N2 physisorption, XPS, NH3-TPD, and tested in the selective catalytic reduction of NO with NH3 (NH3-SCR) [...] Read more.
Copper and iron promoted ZrO2 catalysts were prepared by one-pot synthesis using urea. The studied catalysts were characterized by XRD, N2 physisorption, XPS, NH3-TPD, and tested in the selective catalytic reduction of NO with NH3 (NH3-SCR) in the absence and presence of water vapor under the experimental conditions representative of exhaust gases from stationary sources. The influence of SO2 on catalytic performance was also investigated. Among the studied catalysts, the Fe-Zr sample showed the most promising results in NH3-SCR, being active and highly selective to N2. The addition of SO2 markedly improved NO and NH3 conversions during NH3-SCR in the presence of H2O. The improvement in acidic surface properties is believed to be the cause. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx by NH3)
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13 pages, 3865 KiB  
Article
High Resistance of SO2 and H2O over Monolithic Mn-Fe-Ce-Al-O Catalyst for Low Temperature NH3-SCR
by Shijie Hao, Yandi Cai, Chuanzhi Sun, Jingfang Sun, Changjin Tang and Lin Dong
Catalysts 2020, 10(11), 1329; https://doi.org/10.3390/catal10111329 - 16 Nov 2020
Cited by 12 | Viewed by 2417
Abstract
Monolithic Mn-Fe-Ce-Al-O catalyst with honeycomb cordierite ceramic as a carrier was reported for the first time for low temperature deNOx application. In the reaction of selective catalytic reduction (SCR) of NO with NH3, a NO conversion of above 80% at [...] Read more.
Monolithic Mn-Fe-Ce-Al-O catalyst with honeycomb cordierite ceramic as a carrier was reported for the first time for low temperature deNOx application. In the reaction of selective catalytic reduction (SCR) of NO with NH3, a NO conversion of above 80% at 100 °C was obtained. Notably, the catalyst also showed excellent resistance against SO2 and H2O. About 60% NO conversion was maintained after successive operation in the mixed stream of SO2 and H2O for 168 h. The Brunner−Emmet−Teller (BET) measurement, SEM, EDS, thermogravimetric analysis (TG), FT-IR, and XPS results of the used catalysts indicated that certain amounts of ammonium sulfate was formed on the surface of the catalyst. XPS results revealed that partial of Fe2+ was oxidized to Fe3+ during the reaction process, and Fe2+ species have strong redox ability, which can explain the decrease in activity after reaction. In addition, SO2 and H2O induced a transformation of Ce from Ce4+ to Ce3+ on the surface of the catalyst, which increased the amount of chemisorbed oxygen. Owing to these factors, the addition of Ce and Fe species contributes to excellent resistance of the catalyst to SO2 and H2O. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx by NH3)
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Review

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30 pages, 33501 KiB  
Review
Aftertreatment Technologies for Diesel Engines: An Overview of the Combined Systems
by Ferenc Martinovic, Lidia Castoldi and Fabio Alessandro Deorsola
Catalysts 2021, 11(6), 653; https://doi.org/10.3390/catal11060653 - 21 May 2021
Cited by 35 | Viewed by 9378
Abstract
The abatement of the pollutants deriving from diesel engines in the vehicle sector still represents an interesting scientific and technological challenge due to increasingly limiting regulations. Meeting the stringent limits of NOx and soot emissions requires a catalytic system with great complexity, [...] Read more.
The abatement of the pollutants deriving from diesel engines in the vehicle sector still represents an interesting scientific and technological challenge due to increasingly limiting regulations. Meeting the stringent limits of NOx and soot emissions requires a catalytic system with great complexity, size of units, and number of units, as well as increased fuel consumption. Thus, an after-treatment device for a diesel vehicle requires the use of an integrated catalyst technology for a reduction in the individual emissions of exhaust gas. The representative technologies devoted to the reduction of NOx under lean-burn operation conditions are selective catalytic reduction (SCR) and the lean NOx trap (LNT), while soot removal is mainly performed by filters (DPF). These devices are normally used in sequence, or a combination of them has been proposed to overcome the drawbacks of the individual devices. This review summarizes the current state of NOx and soot abatement strategies. The main focus of this review is on combined technologies for NOx removal (i.e., LNT–SCR) and for the simultaneous removal of NOx and soot, like SCR-on-Filter (SCRoF), in series LNT/DPF and SCR/DPF, and LNT/DPF and SCR/DPF hybrid systems. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx by NH3)
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36 pages, 2112 KiB  
Review
An Overview of Lean Exhaust deNOx Aftertreatment Technologies and NOx Emission Regulations in the European Union
by Tommaso Selleri, Anastasios D. Melas, Ameya Joshi, Dario Manara, Adolfo Perujo and Ricardo Suarez-Bertoa
Catalysts 2021, 11(3), 404; https://doi.org/10.3390/catal11030404 - 23 Mar 2021
Cited by 77 | Viewed by 10693
Abstract
This paper reviews the recent advances in the management of nitrogen oxide (NOx) emissions from the internal combustion engine of light-duty and heavy-duty vehicles, addressing both technical and legal aspects. Particular focus is devoted to the often-virtuous interaction between new legislation imposing more [...] Read more.
This paper reviews the recent advances in the management of nitrogen oxide (NOx) emissions from the internal combustion engine of light-duty and heavy-duty vehicles, addressing both technical and legal aspects. Particular focus is devoted to the often-virtuous interaction between new legislation imposing more restrictions on the permitted pollutant emission levels and new technologies developed in order to meet these restrictions. The review begins first with the American and then European directives promulgated in the 1970s, aimed at limiting emissions of pollutants from road transport vehicles. Particular attention is paid to the introduction of the Euro standards in the European Union for light- and heavy-duty vehicles, used as a legal and time frame reference for the evolution of emission aftertreatment systems (ATSs). The paper also describes governmental approaches implemented for the control of pollutant emissions in circulating vehicles, such as market surveillance and in-service conformity. In parallel, it is explained how the gradual introduction of small-scale devices aimed at the NOx control, such as lean NOx traps (LNTs) systems, and, most of all, the selective catalytic reduction (SCR) of NOx, permitted the application to road-transport vehicles of this ATS, originally designed in larger sizes for industrial usage. The paper reviews chemical processes occurring in SCR systems and their advantages and drawbacks with respect to the pollutant emission limits imposed by the legislation. Their potential side effects are also addressed, such as the emission of extra, not-yet regulated pollutants such as, for example, NH3 and N2O. The NOx, N2O, and NH3 emission level evolution with the various Euro standards for both light- and heavy-duty vehicles are reported in the light of experimental data obtained at the European Commission’s Joint Research Centre. It is observed that the new technologies, boosted by increasingly stricter legal limits, have led in the last two decades to a clear decrease of over one order of magnitude of NOx emissions in Diesel light-duty vehicles, bringing them to the same level as Euro 6 gasoline vehicles (10 mg/km to 20 mg/km in average). On the other hand, an obvious increase in the emissions of both NH3 and N2O is observed in both Diesel and gasoline light-duty vehicles, whereby NH3 emissions in spark-ignition vehicles are mainly linked to two-reaction mechanisms occurring in three-way catalysts after the catalyst light-off and during engine rich-operation. NH3 emissions measured in recent Euro 6 light-duty vehicles amount to a few mg/km for both gasoline and Diesel engines, whereby N2O emissions exceeding a dozen mg/km have been observed in Diesel vehicles only. The present paper can be regarded as part of a general assessment in view of the next EU emission standards, and a discussion on the role the SCR technology may serve as a NOx emission control strategy from lean-burn vehicles. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx by NH3)
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