Special Issue "Aftertreatment DeNOx Systems for Future Light Duty Lean-Burned Emission Regulations"

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

Deadline for manuscript submissions: 30 November 2019.

Special Issue Editors

Guest Editor
Prof. Juan Ramón González-Velasco Website E-Mail
Faculty of Science and Technology, Department of Chemical Engineering, Basque Country University UPV/EHU, Spain
Interests: heterogeneous catalysis, NOx removal in stationary and mobile applications, volatile organic compounds total oxidation, plastic wastes valorization, clean energy production, valorization of CO2
Guest Editor
Assist. Prof. Beñat Pereda-Ayo Website E-Mail
Faculty of Science and Technology, Department of Chemical Engineering, Basque Country University UPV/EHU, Spain
Interests: heterogeneous catalysis, NOx storage and reduction, selective catalytic reduction, valorization of CO2

Special Issue Information

Dear Colleagues,

Future light duty vehicles in Europe and United States are required to be certified owing to progressively more and more stringent regulations. Improving the exhaust aftertreatment systems must be considered as an integral part of the 21st century vehicle development process. The current potential technologies for NOx removal, namely, NOx storage and reduction (NSR) and selective catalytic reduction (SCR), present some limitations and uncertainties for extensive application in light-duty automobiles. The cold phase during the startup of the engine is now heavily weighted, and improving the efficiency of the catalyst during this phase is crucial to meeting the low tail-pipe emission targets. The combination of LNT with SCR catalysts is an open strategy for expanding the temperature window for efficient operation and lowering precious metals loads.

This Special Issue collects original research papers, reviews, and commentaries focused on the challenges for a new generation of DeNOx catalysts—surface chemistry and physics for high efficiency, low-temperature catalysis—and/or aftertreatment architectures with low cost, high NOx removal efficiency, and long durability to meet the ever rigorous NOx emission, with the aim of revealing promising signs that NOx can be reduced significantly below current standards.

Prof. Juan Ramón González-Velasco
Assist. Prof. Beñat Pereda-Ayo
Guest Editors

Manuscript Submission Information

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Keywords

  • NOx removal
  • lean-burn engines exhaust control
  • NOx adsorbers
  • NOx storage and reduction
  • adsorbed intermediate reductants
  • selective catalytic reduction
  • soot removal
  • sulphur resistance
  • hydrothermal resistance

Published Papers (4 papers)

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Research

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Open AccessArticle
Characteristics of Water and Urea–Water Solution Sprays
Catalysts 2019, 9(9), 750; https://doi.org/10.3390/catal9090750 - 06 Sep 2019
Abstract
In spray studies related to selective catalytic reduction (SCR) systems a common approach is to replace the urea–water solution (UWS) with pure water, even though there is very limited detailed information on the spray properties for these two liquids obtained under the same [...] Read more.
In spray studies related to selective catalytic reduction (SCR) systems a common approach is to replace the urea–water solution (UWS) with pure water, even though there is very limited detailed information on the spray properties for these two liquids obtained under the same conditions using the same experimental equipment. Neither is it known how the possible differences in spray properties influence computational fluid dynamics (CFD) simulations. In this study, besides the flow characteristics, we compare both global and local spray parameters measured for UWS and pure water in the same conditions. To our knowledge, this is the first study which examines the influence on the injection process of replacing UWS with water over such a wide range. Moreover, the influence of different spray properties on CFD simulations is also examined. The experimental studies showed differences in almost all considered spray parameters. Moreover, different spray behaviour was noticed in terms of primary break-up. One important finding is that water and UWS sprays do have a similar Sauter mean diameter, but at the same time the droplet size distribution is considerably different. The simulation results indicated noticeable differences in terms of wall film formation; nevertheless, the overall mixing performance was not significantly affected. Full article
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Open AccessArticle
Sulfur Poisoning Effects on Modern Lean NOx Trap Catalysts Components
Catalysts 2019, 9(6), 492; https://doi.org/10.3390/catal9060492 - 28 May 2019
Abstract
In the present work, a series of different materials was investigated in order to enhance the understanding of the role of modern lean NOx trap (LNT) components on the sulfur poisoning and regeneration characteristics. Nine different types of model catalysts were prepared, [...] Read more.
In the present work, a series of different materials was investigated in order to enhance the understanding of the role of modern lean NOx trap (LNT) components on the sulfur poisoning and regeneration characteristics. Nine different types of model catalysts were prepared, which mainly consisted of three compounds: (i) Al2O3, (ii) Mg/Al2O3, and (iii) Mg/Ce/Al2O3 mixed with Pt, Pd, and Pt-Pd. A micro flow reactor and a diffuse reflectance infrared Fourier transform spectrometer (DRIFTS) were employed in order to investigate the evolution and stability of the species formed during SO2 poisoning. The results showed that the addition of palladium and magnesium into the LNT formulation can be beneficial for the catalyst desulfation due mainly to the ability to release the sulfur trapped at relatively low temperatures. This was especially evident for Pd/Mg/Al2O3 model catalyst, which demonstrated an efficient LNT desulfation with low H2 consumption. In contrast, the addition of ceria was found to increase the formation of bulk sulfate species during SO2 poisoning, which requires higher temperatures for the sulfur removal. The noble metal nature was also observed to play an important role on the SOx storage and release properties. Monometallic Pd-based catalysts exhibited the formation of surface palladium sulfate species during SO2 exposure, whereas Pt-Pd bimetallic formulations presented higher stability of the sulfur species formed compared to the corresponding Pt- and Pd-monometallic samples. Full article
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Open AccessArticle
Research on Optimization Design of SCR Nozzle for National VI Heavy Duty Diesel Engine
Catalysts 2019, 9(5), 452; https://doi.org/10.3390/catal9050452 - 16 May 2019
Abstract
For the National VI heavy-duty diesel vehicles, NOx emission regulations are becoming more and more stringent, and the selective catalytic reduction (SCR) system has become a necessary device. The design of the adblue nozzle in the SCR system is especially critical, directly [...] Read more.
For the National VI heavy-duty diesel vehicles, NOx emission regulations are becoming more and more stringent, and the selective catalytic reduction (SCR) system has become a necessary device. The design of the adblue nozzle in the SCR system is especially critical, directly affecting the NOx conversion efficiency and deposit formation. According to the structure of a National VI diesel engine exhaust pipe and SCR system, the nozzle is optimized by computational fluid dynamics (CFD) method to avoid the collision between the urea droplets and the exhaust pipe wall, to ensure that the exhaust gas and the urea droplets are as much as possible in full contact to ensure a sufficient urea pyrolysis. With the optimized nozzle, the NH3 distribution uniformity of the inlet face of the SCR catalyst can increase from 0.58 to 0.92. Additionally, test verifications are implemented based on the spray particle size test and the engine bench tests; the results show that the Sauter mean diameter of the optimized nozzle is more decreased than the initial nozzle and that the NOx conversion efficiency of the World Harmonized Transient Cycle (WHTC) and World Harmonized Stationary Cycle (WHSC) cycle improves by nearly 3%; additionally, it can also avoid deposit formation. Full article
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Review

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Open AccessReview
WO3–V2O5 Active Oxides for NOx SCR by NH3: Preparation Methods, Catalysts’ Composition, and Deactivation Mechanism—A Review
Catalysts 2019, 9(6), 527; https://doi.org/10.3390/catal9060527 - 13 Jun 2019
Abstract
Researchers in the field of the selective catalytic reduction (SCR) of nitrogen oxides (NOx: NO, NO2, or N2O) by NH3 are still greatly challenging the optimization of low-temperature activity and selectivity, high-temperature stability, resistance to alkali [...] Read more.
Researchers in the field of the selective catalytic reduction (SCR) of nitrogen oxides (NOx: NO, NO2, or N2O) by NH3 are still greatly challenging the optimization of low-temperature activity and selectivity, high-temperature stability, resistance to alkali metals and other poisoning agents, such as Hg, As, etc. The present study reviews the research progress, related to the latest 20 years, on WO3–V2O5-based catalysts that are expected to overcome the catalytic performances of the current SCR catalytic devices. In details, the effects of the synthesis methods, chemical composition, type of supports (metal oxides, molecular sieves, and filters), doping elements, or metal oxides added as promoters of WO3–V2O5-based catalysts and, finally, the influence of SO2 and H2O in the reaction mixture are addressed. The importance of understanding the deactivation mechanism in the presence of several poisoning agents is also emphasized, which should be taken into consideration for the design of new catalysts. Full article
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