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Selective Catalytic Reduction: From Basic Science to deNOx Applications
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Selective Catalytic Reduction: From Basic Science to deNOx Applications

A special issue of Catalysts (ISSN 2073-4344). This special issue belongs to the section "Environmental Catalysis".

Deadline for manuscript submissions: closed (31 October 2020) | Viewed by 43028

Special Issue Editors

Dr. Feng Gao

grade E-Mail Website
Guest Editor
Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99354, USA
Interests: heterogeneous catalysis; surface science; catalyst characterization; reaction kinetics; in situ (operando) spectroscopy
Dr. Todd J. Toops

E-Mail Website
Guest Editor
National Transportation Research Center, Oak Ridge National Laboratory, Knoxville, TN 37932, USA
Interests: low-temperature catalysis; passive NOx adsorbers; passive NOx SCR; hydrocarbon traps; oxidation catalysts; particulate filters; deactivation mechanisms; carbon capture and conversion; fuel cells and electrolysis
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The development and commercialization of catalytic processes for remediating toxic emissions from stational sources and from vehicles has been a truly remarkable achievement for the environmental catalysis community. Selective catalytic reduction (SCR) of NOx with ammonia is among the most important and successful such techniques that we have witnessed, evolving from vanadia- to exchanged zeolite-based over the past 50 years. As with other industrialized catalytic processes, basic research aiming at understanding nature of the catalyst active sites, reaction mechanisms, and structure–activity correlations must couple applied studies aiming at efficiency, economics, lifetime, and environmental benignity, etc., of the catalysts. In addition to experimental approaches, we have also witnessed rapid development of computational power in assisting rational catalyst design in the past few decades. This Special Issue welcomes both review and original research articles on all aspects of SCR catalysis, including but not limited to the following topics:

  • Recent advances in the synthesis and optimization of oxide- and zeolite-based SCR catalytic materials;
  • The latest studies on the chemical mechanisms of SCR;
  • Studies on deactivation and regeneration of SCR catalysts;
  • Advances in in situ and operando methods for studying SCR catalyst materials and processes;
  • Recent advances in computational research for SCR research.
Dr. Feng Gao
Dr. Todd J. Toops
Guest Editors

Manuscript Submission Information

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Published Papers (14 papers)

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Editorial

Jump to: Research, Review

3 pages, 182 KiB  
Editorial
Selective Catalytic Reduction: From Basic Science to deNOx Applications
by Feng Gao and Todd J. Toops
Catalysts 2021, 11(2), 250; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11020250 - 12 Feb 2021
Cited by 4 | Viewed by 1765
Abstract
The combustion of coal, petroleum and biofuel for energy generation has resulted in unprecedented benefits to the prosperity of our modern society and will continue to do so in the future [...] Full article
(This article belongs to the Special Issue Selective Catalytic Reduction: From Basic Science to deNOx Applications)

Research

Jump to: Editorial, Review

10 pages, 2834 KiB  
Communication
Ultralow Loading Ruthenium on Alumina Monoliths for Facile, Highly Recyclable Reduction of p-Nitrophenol
by Lorianne R. Shultz, Corbin Feit, Jordan Stanberry, Zhengning Gao, Shaohua Xie, Vasileios A. Anagnostopoulos, Fudong Liu, Parag Banerjee and Titel Jurca
Catalysts 2021, 11(2), 165; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11020165 - 25 Jan 2021
Cited by 6 | Viewed by 2627
Abstract
The pervasive use of toxic nitroaromatics in industrial processes and their prevalence in industrial effluent has motivated the development of remediation strategies, among which is their catalytic reduction to the less toxic and synthetically useful aniline derivatives. While this area of research has [...] Read more.
The pervasive use of toxic nitroaromatics in industrial processes and their prevalence in industrial effluent has motivated the development of remediation strategies, among which is their catalytic reduction to the less toxic and synthetically useful aniline derivatives. While this area of research has a rich history with innumerable examples of active catalysts, the majority of systems rely on expensive precious metals and are submicron- or even a few-nanometer-sized colloidal particles. Such systems provide invaluable academic insight but are unsuitable for practical application. Herein, we report the fabrication of catalysts based on ultralow loading of the semiprecious metal ruthenium on 2–4 mm diameter spherical alumina monoliths. Ruthenium loading is achieved by atomic layer deposition (ALD) and catalytic activity is benchmarked using the ubiquitous para-nitrophenol, NaBH4 aqueous reduction protocol. Recyclability testing points to a very robust catalyst system with intrinsic ease of handling. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction: From Basic Science to deNOx Applications)
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13 pages, 6204 KiB  
Article
AFX Zeolite for Use as a Support of NH3-SCR Catalyst Mining through AICE Joint Research Project of Industries–Academia–Academia
by Masaru Ogura, Yumiko Shimada, Takeshi Ohnishi, Naoto Nakazawa, Yoshihiro Kubota, Toshiyuki Yokoi, Masahiro Ehara, Kenichi Shimizu and Nao Tsunoji
Catalysts 2021, 11(2), 163; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11020163 - 25 Jan 2021
Cited by 8 | Viewed by 3142
Abstract
This paper introduces a joint industries–academia–academia research project started by researchers in several automobile companies and universities working on a single theme. Our first target was to find a zeolite for NH3-SCR, that is, zeolite mining. Zeolite AFX, having the same [...] Read more.
This paper introduces a joint industries–academia–academia research project started by researchers in several automobile companies and universities working on a single theme. Our first target was to find a zeolite for NH3-SCR, that is, zeolite mining. Zeolite AFX, having the same topology of SSZ-16, was found to be the one of the zeolites. SSZ-16 can be synthesized by using an organic structure-directing agent such as 1,1′-tetramethylenebis(1-azonia-4-azabicyclo[2.2.2]octane; Dab-4, resulting in the formation of Al-rich SSZ-16 with Si/Al below five. We found that AFX crystallized by use of N,N,N′,N′-tetraethylbicyclo[2.2.2]oct-7-ene-2,3:5,6-dipyrrolidinium ion, called TEBOP in this study, had the same analog as SSZ-16 having Si/Al around six and a smaller particle size than SSZ-16. The AFX demonstrated a high performance for NH3-SCR as the zeolitic support to load a large number of divalent Cu ionic species with high hydrothermal stability. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction: From Basic Science to deNOx Applications)
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13 pages, 3347 KiB  
Article
The Denitration and Dedusting Behavior of Catalytic Filter and Its Industrial Application in Glass Kilns
by Lin Huangfu, Zhaohui Chen, Changming Li, Xiaolong Yao, Zhiliang Yao, Guangwen Xu, Shiqiu Gao, Xing Huang and Jian Yu
Catalysts 2020, 10(12), 1394; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10121394 - 30 Nov 2020
Cited by 5 | Viewed by 2165
Abstract
The development of efficient materials and processes is a long-term goal for the integrated flue gas purification in industry. In this study, a large-size V-based catalytic filter (L3000 mm × Φ150 mm) was prepared by loading the catalyst emulsion into a blank filter, [...] Read more.
The development of efficient materials and processes is a long-term goal for the integrated flue gas purification in industry. In this study, a large-size V-based catalytic filter (L3000 mm × Φ150 mm) was prepared by loading the catalyst emulsion into a blank filter, which demonstrated excellent performance for simultaneously removing NOx, SOx and dust. The laboratory investigation found that the small catalytic particles, high catalyst loading and low face velocity could improve the DeNOx efficiency, and above 80% NO conversion could be achieved in the temperature range of 250–400 °C on the condition of <300 nm catalytic particle size, >7.41 wt % catalyst loading and <1.00 Nm/min face velocity. The negative effect of SO2/H2O was only observed below 300 °C, and the dust had little negative effects on DeNOx efficiency except for the increase of pressure drop. Moreover, a 90-day industrial test of 2380 catalytic filters over 100,000 Nm3/h of flue gas (0.50 Nm/min) from a glass kiln demonstrated that the removal efficiency of both NOx and SOx could be maintained above 95% with great stability at 320–350 °C, and 99% dust could be removed with a pressure drop of less than 1.40 KPa. The results reported herein indicate the promising application prospect of large-size V-based catalytic filters for integrated flue gas purification in industry. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction: From Basic Science to deNOx Applications)
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12 pages, 3847 KiB  
Article
New Insight into the In Situ SO2 Poisoning Mechanism over Cu-SSZ-13 for the Selective Catalytic Reduction of NOx with NH3
by Yu Qiu, Chi Fan, Changcheng Sun, Hongchang Zhu, Wentian Yi, Jiazhe Chen, Luyao Guo, Xiaoxue Niu, Jianjun Chen, Yue Peng, Tao Zhang and Junhua Li
Catalysts 2020, 10(12), 1391; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10121391 - 29 Nov 2020
Cited by 19 | Viewed by 2608
Abstract
To reveal the nature of SO2 poisoning over Cu-SSZ-13 catalyst under actual exhaust conditions, the catalyst was pretreated at 200 and 500 °C in a flow containing NH3, NO, O2, SO2, and H2O. Brunner−Emmet−Teller [...] Read more.
To reveal the nature of SO2 poisoning over Cu-SSZ-13 catalyst under actual exhaust conditions, the catalyst was pretreated at 200 and 500 °C in a flow containing NH3, NO, O2, SO2, and H2O. Brunner−Emmet−Teller (BET), X-ray diffraction(XRD), thermo gravimetric analyzer (TGA), ultraviolet Raman spectroscopy (UV Raman), temperature-programmed reduction with H2 (H2-TPR), temperature-programmed desorption of NO+O2 (NO+O2-TPD), NH3-TPD, in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), and an activity test were utilized to monitor the changes of Cu-SSZ-13 before and after in situ SO2 poisoning. According to the characterization results, the types and generated amount of sulfated species were directly related to poisoning temperature. Three sulfate species, including (NH4)2SO4, CuSO4, and Al2(SO4)3, were found to form on CZ-S-200, while only the latter two sulfate species were observed over CZ-S-500. Furthermore, SO2 poisoning had a negative effect on low-temperature selective catalytic reduction (SCR) activity, which was mainly due to the sulfation of active sites, including Z2Cu, ZCuOH, and Si-O(H)-Al. In contrast, SO2 poisoning had a positive effect on high-temperature SCR activity, owing to the inhibition of the NH3 oxidation reaction. The above findings may be a useful guideline to design excellent SO2-resistant Cu-based zeolite catalysts. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction: From Basic Science to deNOx Applications)
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14 pages, 4556 KiB  
Article
Promoting Effect of Mn on In Situ Synthesized Cu-SSZ-13 for NH3-SCR
by Jinpeng Du, Jingyi Wang, Xiaoyan Shi, Yulong Shan, Yan Zhang and Hong He
Catalysts 2020, 10(12), 1375; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10121375 - 25 Nov 2020
Cited by 18 | Viewed by 2662
Abstract
The effect of Mn impregnation on the NH3-SCR (selective catalytic reduction of NOx by NH3) activity of in situ synthesized Cu-SSZ-13 was investigated in this work. It was found that Mn addition could efficiently improve the low-temperature activity [...] Read more.
The effect of Mn impregnation on the NH3-SCR (selective catalytic reduction of NOx by NH3) activity of in situ synthesized Cu-SSZ-13 was investigated in this work. It was found that Mn addition could efficiently improve the low-temperature activity of Cu-SSZ-13. The optimal amount of Mn was 5 wt.%, and NOx conversion was improved by more than 20% over a temperature range of 120 °C to 150 °C. SEM (scanning electron microscopy), XRD (X-ray diffraction), N2 adsorption-desorption, H2-TPR (temperature programmed reduction of H2), NH3-TPD (temperature programmed desorption of NH3) and in situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) experiments were conducted to investigate the changes in the zeolite structure, active sites, acid sites and reaction mechanism. The impregnated MnOx species caused a decline in the crystallinity of Cu-SSZ-13 but markedly improved the redox ability. Nitrate and nitrite species were observed in the Mn-modified Cu-SSZ-13, and the formation of these species was thought to cause the observed increase in low-temperature NH3-SCR activity. The results show that the addition of Mn is a promising method for promoting the low-temperature catalytic activity of Cu-SSZ-13. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction: From Basic Science to deNOx Applications)
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22 pages, 8064 KiB  
Article
A Dynamic Model Incorporated with Delay Estimation and Variable Selection for Control of SCR De-NOx Process
by Ze Dong, Ling Li, Laiqing Yan, Ming Sun and Jinsong Li
Catalysts 2020, 10(11), 1364; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10111364 - 23 Nov 2020
Cited by 6 | Viewed by 2291
Abstract
In order to control NH3 injection for the selective catalytic reduction of nitrogen oxide (NOx) denitration (SCR de-NOx) process, a model that can accurately and quickly predict outlet NOx emissions is required. This paper presents a dynamic [...] Read more.
In order to control NH3 injection for the selective catalytic reduction of nitrogen oxide (NOx) denitration (SCR de-NOx) process, a model that can accurately and quickly predict outlet NOx emissions is required. This paper presents a dynamic kernel partial least squares (KPLS) model incorporated with delay estimation and variable selection for outlet NOx emission and investigated control strategy for NH3 injection. First, k-nearest neighbor mutual information (KNN_MI) was used for delay estimation, and the effect of historical data lengths on KNN_MI was taken into account. Bidirectional search based on the change rate of KNN_MI (KNN_MI_CR) was used for variable selection. Delay–time difference update algorithm and feedback correction strategy were proposed. Second, the NH3 injection compensator (NIC) and the outlet NOx emission model constituted a correction controller. Then, its output and the output of the existing controller are added up to suitable NH3 injection. Finally, the KNN_MI_CR method was compared with different algorithms by benchmark dataset. The field data results showed that the KNN_MI_CR method could improve model accuracy for reconstructed samples. The final model can predict outlet NOx emissions in different operating states accurately. The control result not only meets the NOx emissions standard (50 mg/m3) but also keeps high de-NOx efficiency (80%). NH3 injection and NH3 escape are reduced by 11% and 39%. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction: From Basic Science to deNOx Applications)
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15 pages, 12795 KiB  
Article
Investigation of Urea Uniformity with Different Types of Urea Injectors in an SCR System
by Muhammad Khristamto Aditya Wardana, Kwangchul Oh and Ocktaeck Lim
Catalysts 2020, 10(11), 1269; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10111269 - 2 Nov 2020
Cited by 11 | Viewed by 2493
Abstract
Heavy-duty diesel engines in highway use account for more than 40% of total particulate and nitrogen oxide (NOx) emissions around the world. Selective catalytic reduction (SCR) is a method with effective results to reduce this problem. This research deals with problems [...] Read more.
Heavy-duty diesel engines in highway use account for more than 40% of total particulate and nitrogen oxide (NOx) emissions around the world. Selective catalytic reduction (SCR) is a method with effective results to reduce this problem. This research deals with problems in the urea evaporation process and ammonia gas distribution in an SCR system. The studied system used two types of urea injectors to elucidate the quality of ammonia uniformity in the SCR system, and a 12,000-cc heavy-duty diesel engine was used for experimentation to reduce NOx in the system. The uniformity of the generated quantities of ammonia was sampled at the catalyst inlet using a gas sensor. The ammonia samples from the two types of urea injectors were compared in experimental and simulation results, where the simulation conditions were based on experimental parameters and were performed using the commercial CFD (computational fluid dynamics) code of STAR-CCM+. This study produces temperatures of 371 to 374 °C to assist the vaporization phenomena of two injectors, the gas pattern informs the distributions of ammonia in the system, and the high ammonia quantity from the I-type urea injector and high quality of ammonia uniformity from the L-type urea injector can produce different results for NOx reduction efficiency quality after the catalyst process. The investigations showed the performance of two types of injectors and catalysts in the SCR system in a heavy-duty diesel engine. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction: From Basic Science to deNOx Applications)
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17 pages, 3233 KiB  
Article
Sb-Containing Metal Oxide Catalysts for the Selective Catalytic Reduction of NOx with NH3
by Qian Xu, Dandan Liu, Chuchu Wang, Wangcheng Zhan, Yanglong Guo, Yun Guo, Li Wang, Qingping Ke and Minh Ngoc Ha
Catalysts 2020, 10(10), 1154; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10101154 - 8 Oct 2020
Cited by 9 | Viewed by 2280
Abstract
Sb-containing catalysts (SbZrOx (SbZr), SbCeOx (SbCe), SbCeZrOx (SbCeZr)) were prepared by citric acid method and investigated for the selective catalytic reduction (SCR) of NOx with NH3 (NH3-SCR). SbCeZr outperformed SbZr and SbCe and exhibited the highest [...] Read more.
Sb-containing catalysts (SbZrOx (SbZr), SbCeOx (SbCe), SbCeZrOx (SbCeZr)) were prepared by citric acid method and investigated for the selective catalytic reduction (SCR) of NOx with NH3 (NH3-SCR). SbCeZr outperformed SbZr and SbCe and exhibited the highest activity with 80% NO conversion in the temperature window of 202–422 °C. Meanwhile, it also had good thermal stability and resistance against H2O and SO2. Various characterization methods, such as XRD, XPS, H2-TPR, NH3-TPD, and in situ diffuse reflectance infrared Fourier transform (DRIFT), were applied to understand their different behavior in NOx removal. The presence of Sb in the metal oxides led to the difference in acid distribution and redox property, which closely related with the NH3 adsorption and NO oxidation. Brønsted acid and Lewis acid were evenly distributed on SbCe, while Brønsted acid dominated on SbCeZr. Compared with Brønsted acid, Lewis acid was slightly active in NH3-SCR. The competition between NH3 adsorption and NO oxidation was dependent on SbOx and metal oxides, which were found on SbCe while not on SbCeZr. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction: From Basic Science to deNOx Applications)
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15 pages, 18102 KiB  
Article
Investigation of Sulfated Iron-Based Catalysts with Different Sulfate Position for Selective Catalytic Reduction of NOx with NH3
by Baiyu Fan, Ziyin Zhang, Caixia Liu and Qingling Liu
Catalysts 2020, 10(9), 1035; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10091035 - 9 Sep 2020
Cited by 15 | Viewed by 2750
Abstract
The Fe/(SZr) and S(Fe/Zr) sulfated iron-based catalysts, prepared by impregnation methods through changing the loading order of Fe2O3 and SO42− on ZrO2, were investigated on selective catalytic reduction (SCR) of NOx by ammonia. It was [...] Read more.
The Fe/(SZr) and S(Fe/Zr) sulfated iron-based catalysts, prepared by impregnation methods through changing the loading order of Fe2O3 and SO42− on ZrO2, were investigated on selective catalytic reduction (SCR) of NOx by ammonia. It was studied that the existent forms of Fe2O3 and SO42− on the surface of catalysts were affected by the loading order. The Fe/(SZr) catalyst surface had isolated Fe2O3 and SO42− species and followed both the L-H mechanism and the E-R mechanism, whereas the S(Fe/Zr) catalyst contained SO42− specie and sulfate only and mainly followed the E-R pathway. These factors affected the redox ability and NH3 adsorption, which might be key to the SCR reaction. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction: From Basic Science to deNOx Applications)
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Review

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20 pages, 4602 KiB  
Review
Recent Understanding of Low-Temperature Copper Dynamics in Cu-Chabazite NH3-SCR Catalysts
by Huarong Lei, Valentina Rizzotto, Anqi Guo, Daiqi Ye, Ulrich Simon and Peirong Chen
Catalysts 2021, 11(1), 52; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11010052 - 1 Jan 2021
Cited by 15 | Viewed by 4254
Abstract
Dynamic motion of NH3-solvated Cu sites in Cu-chabazite (Cu-CHA) zeolites, which are the most promising and state-of-the-art catalysts for ammonia-assisted selective reduction of NOx (NH3-SCR) in the aftertreatment of diesel exhausts, represents a unique phenomenon linking heterogeneous and [...] Read more.
Dynamic motion of NH3-solvated Cu sites in Cu-chabazite (Cu-CHA) zeolites, which are the most promising and state-of-the-art catalysts for ammonia-assisted selective reduction of NOx (NH3-SCR) in the aftertreatment of diesel exhausts, represents a unique phenomenon linking heterogeneous and homogeneous catalysis. This review first summarizes recent advances in the theoretical understanding of such low-temperature Cu dynamics. Specifically, evidence of both intra-cage and inter-cage Cu motions, given by ab initio molecular dynamics (AIMD) or metadynamics simulations, will be highlighted. Then, we will show how, among others, synchrotron-based X-ray spectroscopy, vibrational and optical spectroscopy (diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) and diffuse reflection ultraviolet-visible spectroscopy (DRUVS)), electron paramagnetic spectroscopy (EPR), and impedance spectroscopy (IS) can be combined and complement each other to follow the evolution of coordinative environment and the local structure of Cu centers during low-temperature NH3-SCR reactions. Furthermore, the essential role of Cu dynamics in the tuning of low-temperature Cu redox, in the preparation of highly dispersed Cu-CHA catalysts by solid-state ion exchange method, and in the direct monitoring of NH3 storage and conversion will be presented. Based on the achieved mechanistic insights, we will discuss briefly the new perspectives in manipulating Cu dynamics to improve low-temperature NH3-SCR efficiency as well as in the understanding of other important reactions, such as selective methane-to-methanol oxidation and ethene dimerization, catalyzed by metal ion-exchanged zeolites. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction: From Basic Science to deNOx Applications)
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19 pages, 2958 KiB  
Review
Recent Progress on Improving Low-Temperature Activity of Vanadia-Based Catalysts for the Selective Catalytic Reduction of NOx with Ammonia
by Zhihua Lian, Yingjie Li, Wenpo Shan and Hong He
Catalysts 2020, 10(12), 1421; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10121421 - 4 Dec 2020
Cited by 28 | Viewed by 3219
Abstract
Selective catalytic reduction of NOx with NH3 (NH3-SCR) has been successfully applied to abate NOx from diesel engines and coal-fired industries on a large scale. Although V2O5-WO3(MoO3)/TiO2 catalysts have [...] Read more.
Selective catalytic reduction of NOx with NH3 (NH3-SCR) has been successfully applied to abate NOx from diesel engines and coal-fired industries on a large scale. Although V2O5-WO3(MoO3)/TiO2 catalysts have been utilized in commercial applications, novel vanadia-based catalysts have been recently developed to meet the increasing requirements for low-temperature catalytic activity. In this article, recent progress on the improvement of the low-temperature activity of vanadia-based catalysts is reviewed, including modification with metal oxides and nonmetal elements and the use of novel supports, different synthesis methods, metal vanadates and specific structures. Investigation of the NH3-SCR reaction mechanism, especially at low temperatures, is also emphasized. Finally, for low-temperature NH3-SCR, some suggestions are given regarding the opportunities and challenges of vanadia-based catalysts in future research. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction: From Basic Science to deNOx Applications)
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33 pages, 6659 KiB  
Review
Fe-Exchanged Small-Pore Zeolites as Ammonia Selective Catalytic Reduction (NH3-SCR) Catalysts
by Feng Gao
Catalysts 2020, 10(11), 1324; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10111324 - 14 Nov 2020
Cited by 31 | Viewed by 4149
Abstract
Cu-exchanged small-pore zeolites have been extensively studied in the past decade as state-of-the-art selective catalytic reduction (SCR) catalysts for diesel engine exhaust NOx abatement for the transportation industry. During this time, Fe-exchanged small-pore zeolites, e.g., Fe/SSZ-13, Fe/SAPO-34, Fe/SSZ-39 and high-silica Fe/LTA, have also [...] Read more.
Cu-exchanged small-pore zeolites have been extensively studied in the past decade as state-of-the-art selective catalytic reduction (SCR) catalysts for diesel engine exhaust NOx abatement for the transportation industry. During this time, Fe-exchanged small-pore zeolites, e.g., Fe/SSZ-13, Fe/SAPO-34, Fe/SSZ-39 and high-silica Fe/LTA, have also been investigated but much less extensively. In comparison to their Cu-exchanged counterparts, such Fe/zeolite catalysts display inferior low-temperature activities, but improved stability and high-temperature SCR selectivities. Such characteristics entitle these catalysts to be considered as key components of highly efficient emission control systems to improve the overall catalyst performance. In this short review, recent studies on Fe-exchanged small-pore zeolite SCR catalysts are summarized, including (1) the synthesis of small-pore Fe/zeolites; (2) nature of the SCR active Fe species in these catalysts as determined by experimental and theoretical approaches, including Fe species transformation during hydrothermal aging; (3) SCR reactions and structure-function correlations; and (4) a few aspects on industrial applications. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction: From Basic Science to deNOx Applications)
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18 pages, 5346 KiB  
Review
The Latest Research Progress of NH3-SCR in the SO2 Resistance of the Catalyst in Low Temperatures for Selective Catalytic Reduction of NOx
by Caixia Liu, Huijun Wang, Ziyin Zhang and Qingling Liu
Catalysts 2020, 10(9), 1034; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10091034 - 9 Sep 2020
Cited by 28 | Viewed by 5285
Abstract
The selective catalytic reduction (SCR) has been widely used in industrial denitrification owing to its high denitrification efficiency, low operating costs, and simple operating procedures. However, coal containing a large amount of sulfur will produce SO2 during combustion, which makes the catalyst [...] Read more.
The selective catalytic reduction (SCR) has been widely used in industrial denitrification owing to its high denitrification efficiency, low operating costs, and simple operating procedures. However, coal containing a large amount of sulfur will produce SO2 during combustion, which makes the catalyst easy to be deactivated, thus limiting the application of this technology. This review summarizes the latest NH3-SCR reaction mechanisms and the deactivation mechanism of catalyst in SO2-containing flue gas. Some strategies are summarized for enhancing the poison-resistance through modification, improvement of support, the preparation of complex oxide catalyst, optimizing the preparation methods, and acidification. The mechanism of improving sulfur resistance of catalysts at low temperatures is summarized, and the further development of the catalyst is also prospected. This paper could provide a reference and guidance for the development of SO2 resistance of the catalyst at low temperatures. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction: From Basic Science to deNOx Applications)
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