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Present Challenges in Catalytic Emission Control for Internal Combustion Engines
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Present Challenges in Catalytic Emission Control for Internal Combustion Engines

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

Deadline for manuscript submissions: closed (31 March 2021) | Viewed by 35774

Special Issue Editors

Dr. Maria Casapu

E-Mail Website
Guest Editor
Institute for Chemical Technology and Polymer Chemistry, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
Interests: heterogeneous catalysis, environmental catalysis, operando spectroscopy, nanoparticles, zeolites
Dr. Dmitry E. Doronkin

E-Mail Website
Guest Editor
Institute of Catalysis Research and Technology (IKFT), Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany
Interests: heterogeneous catalysis, exhaust gas catalysis, energy-related catalysis, X-ray absorption spectroscopy, zeolites, nanoparticles

Special Issue Information

Dear Colleagues,

Despite the increasing market share of electric vehicles, internal combustion engines continue to be widely used in numerous sectors, ranging from transportation to energy production. Numerous efforts are still invested to enhance engine efficiency and decrease CO2 emissions. Concurrently, further improvement of the catalytic exhaust gas aftertreatment system remains a high priority. In particular, knowledge-based catalyst development is regarded as the ultimate approach for attaining near-zero pollutant emissions.

This Special Issue on “Present challenges in catalytic emission control for internal combustion engines” is aimed at providing an overview on state-of-the-art catalyst characterization, performance, deactivation, and reactivation for different classes of catalysts applied to the exhausts of diesel, gasoline, or natural gas engines. The contributions to the Special Issue should preferentially include systematic and comprehensive studies for elucidating mechanistic aspects and deriving structure–activity correlations. Equally important are the contributions describing recent advances in catalyst modeling and simulation.

Dr. Maria Casapu
Dr. Dmitry E. Doronkin
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Catalysts is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Emission control
  • Exhaust gas aftertreatment
  • Three-way catalysts
  • Diesel oxidation catalysts
  • CH4 oxidation catalysts
  • Selective catalytic reduction
  • NOx storage reduction
  • Particulate filters
  • Catalyst deactivation
  • Kinetic modeling

Published Papers (13 papers)

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Editorial

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3 pages, 156 KiB  
Editorial
Present Challenges in Catalytic Emission Control for Internal Combustion Engines
by Dmitry E. Doronkin and Maria Casapu
Catalysts 2021, 11(9), 1019; https://doi.org/10.3390/catal11091019 - 24 Aug 2021
Cited by 3 | Viewed by 1593
Abstract
Mobility in the modern world relies on heterogeneous catalysis [...] Full article
(This article belongs to the Special Issue Present Challenges in Catalytic Emission Control for Internal Combustion Engines)

Research

Jump to: Editorial

11 pages, 1474 KiB  
Article
The H2O Effect on Cu Speciation in Cu-CHA-Catalysts for NH3-SCR Probed by NH3 Titration
by Roberta Villamaina, Federica Gramigni, Umberto Iacobone, Shaojun Liu, Isabella Nova, Enrico Tronconi, Maria Pia Ruggeri, Jillian Collier, Andrew P. E. York and David Thompsett
Catalysts 2021, 11(7), 759; https://doi.org/10.3390/catal11070759 - 23 Jun 2021
Cited by 10 | Viewed by 2171
Abstract
The present work is focused on the effect of water on NH3 adsorption over Cu-CHA SCR catalysts. For this purpose, samples characterized by different SAR (SiO2/Al2O3) ratios and Cu loadings were studied under both dry and [...] Read more.
The present work is focused on the effect of water on NH3 adsorption over Cu-CHA SCR catalysts. For this purpose, samples characterized by different SAR (SiO2/Al2O3) ratios and Cu loadings were studied under both dry and wet conditions. H2O adversely affects NH3 adsorption on Lewis acid sites (Cu ions) over all the tested catalysts, as indicated by the decreased NH3 desorption at low temperature during TPD. Interestingly, the NH3/Cu ratio, herein regarded as an index for the speciation of Cu cations, fell in the range of 3–4 (in the presence of gaseous NH3) or 1–2 (no gaseous NH3) in dry conditions, in line with the formation of different NH3-solvated Cu species (e.g., [CuII(NH3)4]2+ and [CuII(OH)(NH3)3]+ with gaseous NH3, [Z2CuII(NH3)2]2+ and [ZCuII(OH)(NH3)]+ without gaseous NH3). When H2O was fed to the system, on the contrary, the NH3/Cu ratio was always close to 3 (or 1), while the Brønsted acidity was slightly increased. These results are consistent both with competition between H2O and NH3 for adsorption on Lewis sites and with the hydrolysis of a fraction of Z2CuII species into ZCuIIOH. Full article
(This article belongs to the Special Issue Present Challenges in Catalytic Emission Control for Internal Combustion Engines)
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21 pages, 5029 KiB  
Article
The Impact of Lanthanum and Zeolite Structure on Hydrocarbon Storage
by Rasmus Jonsson, Phuoc Hoang Ho, Aiyong Wang, Magnus Skoglundh and Louise Olsson
Catalysts 2021, 11(5), 635; https://doi.org/10.3390/catal11050635 - 15 May 2021
Cited by 7 | Viewed by 2700
Abstract
Hydrocarbon traps can be used to bridge the temperature gap from the cold start of a vehicle until the exhaust after-treatment catalyst has reached its operating temperature. In this work, we investigate the effect of zeolite structure (ZSM-5, BEA, SSZ-13) and the effect [...] Read more.
Hydrocarbon traps can be used to bridge the temperature gap from the cold start of a vehicle until the exhaust after-treatment catalyst has reached its operating temperature. In this work, we investigate the effect of zeolite structure (ZSM-5, BEA, SSZ-13) and the effect of La addition to H-BEA and H-ZSM-5 on the hydrocarbon storage capacity by temperature-programmed desorption and DRIFT spectroscopy. The results show that the presence of La has a significant effect on the adsorption characteristics of toluene on the BEA-supported La materials. A low loading of La onto zeolite BEA (2% La-BEA) improves not only the toluene adsorption capacity but also the retention of toluene. However, a higher loading of La results in a decrease in the adsorbed amount of toluene, which likely is due to partial blocking of the pore of the support. High loadings of La in BEA result in a contraction of the unit cell of the zeolite as evidenced by XRD. A synergetic effect of having simultaneously different types of hydrocarbons (toluene, propene, and propane) in the feed is found for samples containing ZSM-5, where the desorption temperature of propane increases, and the quantity that desorbed increases by a factor of four. This is found to be due to the interaction between toluene and propane inside the structure of the zeolite. Full article
(This article belongs to the Special Issue Present Challenges in Catalytic Emission Control for Internal Combustion Engines)
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13 pages, 2823 KiB  
Article
Insights into the Structural Dynamics of Pt/CeO2 Single-Site Catalysts during CO Oxidation
by Paolo Dolcet, Florian Maurer, Maria Casapu and Jan-Dierk Grunwaldt
Catalysts 2021, 11(5), 617; https://doi.org/10.3390/catal11050617 - 11 May 2021
Cited by 6 | Viewed by 2880
Abstract
Despite their high atomic dispersion, single site catalysts with Pt supported on CeO2 were found to have a low activity during oxidation reactions. In this study, we report the behavior of Pt/CeO2 single site catalyst under more complex gas mixtures, including [...] Read more.
Despite their high atomic dispersion, single site catalysts with Pt supported on CeO2 were found to have a low activity during oxidation reactions. In this study, we report the behavior of Pt/CeO2 single site catalyst under more complex gas mixtures, including CO, C3H6 and CO/C3H6 oxidation in the absence or presence of water. Our systematic operando high-energy resolution-fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) spectroscopic study combined with multivariate curve resolution with alternating least squares (MCR-ALS) analysis identified five distinct states in the Pt single site structure during CO oxidation light-off. After desorption of oxygen and autoreduction of Pt4+ to Pt2+ due to the increase of temperature, CO adsorbs and reduces Pt2+ to Ptδ+ and assists its migration with final formation of PtxΔ+ clusters. The derived structure–activity relationships indicate that partial reduction of Pt single sites is not sufficient to initiate the conversion of CO. The reaction proceeds only after the regrouping of several noble metal atoms in small clusters, as these entities are probably able to influence the mobility of the oxygen at the interface with ceria. Full article
(This article belongs to the Special Issue Present Challenges in Catalytic Emission Control for Internal Combustion Engines)
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19 pages, 5187 KiB  
Article
Particle Number Emissions of a Euro 6d-Temp Gasoline Vehicle under Extreme Temperatures and Driving Conditions
by Barouch Giechaskiel, Victor Valverde, Anastasios Kontses, Anastasios Melas, Giorgio Martini, Andreas Balazs, Jon Andersson, Zisis Samaras and Panagiota Dilara
Catalysts 2021, 11(5), 607; https://doi.org/10.3390/catal11050607 - 10 May 2021
Cited by 22 | Viewed by 3496
Abstract
With the introduction of gasoline particulate filters (GPFs), the particle number (PN) emissions of gasoline direct-injection (GDI) vehicles are below the European regulatory limit of 6 × 1011 p/km under certification conditions. Nevertheless, concerns have been raised regarding emission levels at the [...] Read more.
With the introduction of gasoline particulate filters (GPFs), the particle number (PN) emissions of gasoline direct-injection (GDI) vehicles are below the European regulatory limit of 6 × 1011 p/km under certification conditions. Nevertheless, concerns have been raised regarding emission levels at the boundaries of ambient and driving conditions of the real-driving emissions (RDE) regulation. A Euro 6d-Temp GDI vehicle with a GPF was tested on the road and in the laboratory with cycles simulating congested urban traffic, dynamic driving, and towing a trailer uphill at 85% of maximum payload. The ambient temperatures covered a range from −30 to 50 °C. The solid PN emissions were 10 times lower than the PN limit under most conditions and temperatures. Only dynamic driving that regenerated the filter passively, and for the next cycle resulted in relatively high emissions although they were still below the limit. The results of this study confirmed the effectiveness of GPFs in controlling PN emissions under a wide range of conditions. Full article
(This article belongs to the Special Issue Present Challenges in Catalytic Emission Control for Internal Combustion Engines)
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19 pages, 10796 KiB  
Article
Catalyst Modeling Challenges for Electrified Powertrains
by Thomas Souliotis, Grigorios Koltsakis and Zissis Samaras
Catalysts 2021, 11(5), 539; https://doi.org/10.3390/catal11050539 - 22 Apr 2021
Cited by 6 | Viewed by 2474
Abstract
To meet the upcoming CO2 reduction challenges, the further electrification of vehicle powertrains is indispensable. In combination with the post-Euro 6 requirements for criteria pollutants, the exhaust system is expected to be more complex to allow for extremely low emissions under all [...] Read more.
To meet the upcoming CO2 reduction challenges, the further electrification of vehicle powertrains is indispensable. In combination with the post-Euro 6 requirements for criteria pollutants, the exhaust system is expected to be more complex to allow for extremely low emissions under all driving conditions, potentially involving technologies such as electrical heating and phase-change materials. The longer ‘zero-flow’ operation of the exhaust system in hybrid applications and the associated light-out risk have demanding accuracy requirements for heat loss calculations and require additional thermal management strategies. This paper discusses the additional challenges posed with regard to catalyst modeling in the boundary conditions of electrified vehicles and the necessary improvements that go beyond the state-of-the-art techniques. Most of the necessary improvements are linked to advanced 3D modeling of the exhaust system components accounting for free convection and radiative heat transfer. Modeling of electrically assisted heating is demonstrated using a new approach involving a combined 3D electrical–thermal solver. Heat retention technologies with use of phase-change materials are also accounted for in these new-generation models. Finally, the need for a tighter integration of these high-fidelity models into a vehicle simulation framework is discussed. Full article
(This article belongs to the Special Issue Present Challenges in Catalytic Emission Control for Internal Combustion Engines)
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15 pages, 9172 KiB  
Article
Analysis of Ion-Exchanged ZSM-5, BEA, and SSZ-13 Zeolite Trapping Materials under Realistic Exhaust Conditions
by Todd J. Toops, Andrew J. Binder, Pranaw Kunal, Eleni A. Kyriakidou and Jae-Soon Choi
Catalysts 2021, 11(4), 449; https://doi.org/10.3390/catal11040449 - 31 Mar 2021
Cited by 18 | Viewed by 4491
Abstract
An industry-defined evaluation protocol was used to evaluate the hydrocarbon trapping (HCT) and passive NOx adsorption (PNA) potential for BEA, ZSM-5, and SSZ-13 zeolites with ion-exchanged Pd or Ag. All materials underwent 700 °C degreening prior to exposure to an industry-derived protocol gas [...] Read more.
An industry-defined evaluation protocol was used to evaluate the hydrocarbon trapping (HCT) and passive NOx adsorption (PNA) potential for BEA, ZSM-5, and SSZ-13 zeolites with ion-exchanged Pd or Ag. All materials underwent 700 °C degreening prior to exposure to an industry-derived protocol gas stream, which included NOx, ethylene, toluene, and decane as measured trapping species as well as common exhaust gasses CO, H2O, O2, CO2, and H2. Evaluation showed that BEA and ZSM-5 zeolites were effective at trapping hydrocarbons (HCs), as saturation was not achieved after 30 min of exposure. SSZ-13 also stored HCs but was only able to adsorb 20–25% compared to BEA and ZSM-5. The presence of Ag or Pd did not impact the overall HC uptake, particularly in the first three minutes. Pd/zeolites had significantly lower THC release temperature, and it aided in the conversion of the released HCs; Ag only had a moderate effect in both areas. With respect to NOx adsorption, the level of uptake was much lower than HCs on all samples, and Ag or Pd was necessary with Pd being notably more effective. Additionally, only Pd/ZSM-5 and Pd/SSZ-13 continue to store a portion of the NOx above 200 °C, which is critical for downstream selective catalytic NOx reduction (SCR). Hydrothermal aging (800 °C for 50 h) of a subset of the samples were performed: BEA, Pd/BEA, ZSM-5, Pd/ZSM-5, and Pd/SSZ-13. There was a minimal effect on the HC storage, ~10% reduction in capacity with no effect on release temperature; however, only Pd/SSZ-13 showed significant NOx storage after aging. Full article
(This article belongs to the Special Issue Present Challenges in Catalytic Emission Control for Internal Combustion Engines)
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14 pages, 2155 KiB  
Article
Effects of CO and H2O Co-Feed on the Adsorption and Oxidation Properties of a Pd/BEA Hydrocarbon Trap
by Ryan Zelinsky and William S. Epling
Catalysts 2021, 11(3), 348; https://doi.org/10.3390/catal11030348 - 8 Mar 2021
Cited by 4 | Viewed by 2199
Abstract
Hydrocarbon traps for exhaust emissions control adsorb hydrocarbons in low temperature exhaust and release them as the exhaust warms up. In this work, a Pd/BEA hydrocarbon trap was tested under lean exhaust conditions using ethylene and dodecane as model hydrocarbons. Ethylene uptake was [...] Read more.
Hydrocarbon traps for exhaust emissions control adsorb hydrocarbons in low temperature exhaust and release them as the exhaust warms up. In this work, a Pd/BEA hydrocarbon trap was tested under lean exhaust conditions using ethylene and dodecane as model hydrocarbons. Ethylene uptake was partially inhibited by CO and H2O when fed separately. When both were added, the loss in ethylene uptake was 90% relative to the condition with no H2O or CO. Dodecane uptake was unchanged under all conditions tested. During a temperature ramp, ethylene desorbed and was combusted to CO2 and H2O over active Pd centers. Further, oxidation light-off of dodecane generated an exotherm which caused rapid desorption of the remaining hydrocarbon species from the zeolite. For both hydrocarbons, CO co-feed led to a decreased oxidation light-off temperature, and therefore lower desorption temperature. By pretreating the catalyst in CO and H2O at 80 °C, and even after removing CO from the feed, the enhanced oxidation light-off behavior was observed. DRIFTS characterization shows that some form of oxidized Pd was reducible to Pd0 by CO at 80 °C only in the presence of H2O. Further, this reduction appears reversible by high temperature oxygen treatment. We speculate that this reduced Pd phase serves as the active site for low temperature hydrocarbon oxidation. Full article
(This article belongs to the Special Issue Present Challenges in Catalytic Emission Control for Internal Combustion Engines)
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17 pages, 1851 KiB  
Article
The Impact of Pressure and Hydrocarbons on NOx Abatement over Cu- and Fe-Zeolites at Pre-Turbocharger Position
by Deniz Zengel, Simon Barth, Maria Casapu and Jan-Dierk Grunwaldt
Catalysts 2021, 11(3), 336; https://doi.org/10.3390/catal11030336 - 6 Mar 2021
Cited by 8 | Viewed by 1886
Abstract
Positioning the catalysts in front of the turbocharger has gained interest over recent years due to the earlier onset temperature and positive effect of elevated pressure. However, several challenges must be overcome, like presence of higher pollutant concentrations due to the absence or [...] Read more.
Positioning the catalysts in front of the turbocharger has gained interest over recent years due to the earlier onset temperature and positive effect of elevated pressure. However, several challenges must be overcome, like presence of higher pollutant concentrations due to the absence or insufficient diesel oxidation catalyst volume at this location. In this context, our study reports a systematic investigation on the effect of pressure and various hydrocarbons during selective catalytic reduction (SCR) of NOx with NH3 over the zeolite-based catalysts Fe-ZSM-5 and Cu-SSZ-13. Using a high-pressure catalyst test bench, the catalytic activity of both zeolite catalysts was measured in the presence and absence of a variety of hydrocarbons under pressures and temperatures resembling the conditions upstream of the turbocharger. The results obtained showed that the hydrocarbons are incompletely converted over both catalysts, resulting in numerous byproducts. The emission of hydrogen cyanide seems to be particularly problematic. Although the increase in pressure was able to improve the oxidation of hydrocarbons and significantly reduce the formation of HCN, sufficiently low emissions could only be achieved at high temperatures. Regarding the NOx conversion, a boost in activity was obtained by increasing the pressure compared to atmospheric reaction conditions, which compensated the negative effect of hydrocarbons on the SCR activity. Full article
(This article belongs to the Special Issue Present Challenges in Catalytic Emission Control for Internal Combustion Engines)
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18 pages, 5186 KiB  
Article
Effects of Hydrothermal Aging on CO and NO Oxidation Activity over Monometallic and Bimetallic Pt-Pd Catalysts
by Jochen Schütz, Heike Störmer, Patrick Lott and Olaf Deutschmann
Catalysts 2021, 11(3), 300; https://doi.org/10.3390/catal11030300 - 25 Feb 2021
Cited by 22 | Viewed by 3017
Abstract
By combining scanning transmission electron microscopy, CO chemisorption, and energy dispersive X-ray spectroscopy with CO and NO oxidation light-off measurements we investigated deactivation phenomena of Pt/Al2O3, Pd/Al2O3, and Pt-Pd/Al2O3 model diesel oxidation [...] Read more.
By combining scanning transmission electron microscopy, CO chemisorption, and energy dispersive X-ray spectroscopy with CO and NO oxidation light-off measurements we investigated deactivation phenomena of Pt/Al2O3, Pd/Al2O3, and Pt-Pd/Al2O3 model diesel oxidation catalysts during stepwise hydrothermal aging. Aging induces significant particle sintering that results in a decline of the catalytic activity for all catalyst formulations. While the initial aging step caused the most pronounced deactivation and sintering due to Ostwald ripening, the deactivation rates decline during further aging and the catalyst stabilizes at a low level of activity. Most importantly, we observed pronounced morphological changes for the bimetallic catalyst sample: hydrothermal aging at 750 °C causes a stepwise transformation of the Pt-Pd alloy via core-shell structures into inhomogeneous agglomerates of palladium and platinum. Our study shines a light on the aging behavior of noble metal catalysts under industrially relevant conditions and particularly underscores the highly complex transformation of bimetallic Pt-Pd diesel oxidation catalysts during hydrothermal treatment. Full article
(This article belongs to the Special Issue Present Challenges in Catalytic Emission Control for Internal Combustion Engines)
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15 pages, 3085 KiB  
Article
Characterization of the Evolution of Noble Metal Particles in a Commercial Three-Way Catalyst: Correlation between Real and Simulated Ageing
by Mattia Giuliano, Maria Carmen Valsania, Pierfrancesco Ticali, Enrico Sartoretti, Sara Morandi, Samir Bensaid, Gabriele Ricchiardi and Mauro Sgroi
Catalysts 2021, 11(2), 247; https://doi.org/10.3390/catal11020247 - 12 Feb 2021
Cited by 10 | Viewed by 2334
Abstract
Ageing of automotive catalysts is associated to a loss of their functionality and ultimately to a waste of precious resources. For this reason, understanding catalyst ageing phenomena is necessary for the design of long lasting efficient catalysts. The present work has the purpose [...] Read more.
Ageing of automotive catalysts is associated to a loss of their functionality and ultimately to a waste of precious resources. For this reason, understanding catalyst ageing phenomena is necessary for the design of long lasting efficient catalysts. The present work has the purpose of studying in depth all the phenomena that occur during ageing, in terms of morphological modification and deactivation of the active materials: precious metal particles and oxidic support. The topic was deeply investigated using specific methodologies (FT-IR, CO chemisorption, FE-SEM) in order to understand the behavior of metals and support, in terms of their surface properties, morphology and dispersion in the washcoat material. A series of commercial catalysts, aged in different conditions, have been analyzed, in order to find correlations between real and simulated ageing conditions. The characterization highlights a series of phenomena linked to the deactivation of the catalysts. Pd nanoparticles undergo a rapid agglomeration, exhibiting a quick loss of dispersion and of active sites with an increase of particles size. The evolution of the support allows highlighting also the contribution of chemical ageing effects. These results were also correlated with performance tests executed on synthetic gas bench, underlining a good correspondence between vehicle and laboratory aged samples and the contribution of chemical poisoning to vehicle aged ones. The collected data are crucial for the development of accelerated laboratory ageing protocols, which are instrumental for the development and testing of long lasting abatement systems. Full article
(This article belongs to the Special Issue Present Challenges in Catalytic Emission Control for Internal Combustion Engines)
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25 pages, 2215 KiB  
Article
High Surface Area VOx/TiO2/SBA-15 Model Catalysts for Ammonia SCR Prepared by Atomic Layer Deposition
by Jun Shen and Christian Hess
Catalysts 2020, 10(12), 1386; https://doi.org/10.3390/catal10121386 - 28 Nov 2020
Cited by 13 | Viewed by 2990
Abstract
The mode of operation of titania-supported vanadia (VOx) catalysts for NOx abatement using ammonia selective catalytic reduction (NH3-SCR) is still vigorously debated. We introduce a new high surface area VOx/TiO2/SBA-15 model catalyst system based [...] Read more.
The mode of operation of titania-supported vanadia (VOx) catalysts for NOx abatement using ammonia selective catalytic reduction (NH3-SCR) is still vigorously debated. We introduce a new high surface area VOx/TiO2/SBA-15 model catalyst system based on mesoporous silica SBA-15 making use of atomic layer deposition (ALD) for controlled synthesis of titania and vanadia multilayers. The bulk and surface structure is characterized by X-ray diffraction (XRD), UV-vis and Raman spectroscopy, as well as X-ray photoelectron spectroscopy (XPS), revealing the presence of dispersed surface VOx species on amorphous TiO2 domains on SBA-15, forming hybrid Si–O–V and Ti–O–V linkages. Temperature-dependent analysis of the ammonia SCR catalytic activity reveals NOx conversion levels of up to ~60%. In situ and operando diffuse reflection IR Fourier transform (DRIFT) spectroscopy shows N–Hstretching modes, representing adsorbed ammonia and -NH2 and -NH intermediate structures on Bronsted and Lewis acid sites. Partial Lewis acid sites with adjacent redox sites are proposed as the active sites and desorption of product molecules as the rate-determining step at low temperature. The high NOx conversion is attributed to the presence of highly dispersed VOx species and the moderate acidity of VOx supported on TiO2/SBA-15. Full article
(This article belongs to the Special Issue Present Challenges in Catalytic Emission Control for Internal Combustion Engines)
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11 pages, 1490 KiB  
Article
Self-Regeneration Effect of Three-Way Catalysts during Thermal Aging Procedure
by Evgeny A. Alikin, Sergey P. Denisov, Konstantin V. Bubnov and Aleksey A. Vedyagin
Catalysts 2020, 10(11), 1257; https://doi.org/10.3390/catal10111257 - 30 Oct 2020
Cited by 3 | Viewed by 2149
Abstract
One of the most important features of the three-way catalysts is their long-term stability. However, quite often, promising catalytic compositions with excellent activity become deactivated after a relatively short period of exploitation due to various reasons. Therefore, a study on the onboard regeneration [...] Read more.
One of the most important features of the three-way catalysts is their long-term stability. However, quite often, promising catalytic compositions with excellent activity become deactivated after a relatively short period of exploitation due to various reasons. Therefore, a study on the onboard regeneration of the deactivated three-way catalysts remains its actuality. The present work is mainly focused on the self-regeneration effect of the rhodium-containing component. Aging of the catalysts in the standard and model engine braking regimes revealed the difference in the catalytic performance. Deactivated rhodium species turned to the active state as a result of rapid cooling in air flow from 1200 to 600 °C. The regenerated catalyst shows improved activity towards NOx reduction and, therefore, widened operation window, which indicates higher accessibility of the rhodium species. X-ray diffraction analysis of the aged catalysts does not reveal any noticeable phase changes. Contrary, significant changes in the Rh oxidation state were registered by X-ray photoelectron spectroscopy. The observed effect opens new horizons for the development of the onboard purification systems with prolonged exploitation lifetime. Full article
(This article belongs to the Special Issue Present Challenges in Catalytic Emission Control for Internal Combustion Engines)
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