| 1. |
- Bergman, Susanna L., et al.
(author)
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In-situ studies of oxidation/reduction of copper in Cu-CHA SCR catalysts: Comparison of fresh and SO2-poisoned catalysts
- 2020
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In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 269
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Journal article (peer-reviewed)abstract
- SO2-poisoning results in deactivation of Cu-CHA SCR under standard SCR conditions; however regeneration at 700 °C completely restores the SCR performance. To understand the nature of these effects, Cu-species in the fresh and poisoned catalysts were characterized by in-situ temperature-dependent time-resolved Cu K-edge X-ray absorption spectroscopy using the multivariate curve resolution alternating least squares (MCR-ALS) approach and continuous Cauchy wavelet transforms. The extracted chemically-meaningful reference spectra of Cu-species were analyzed by DFT-assisted XANES calculations. Cu-bisulfates were found as the most energetically favorable poisoned Cu-species. The response of Cu-species to a reducing environment differs in the fresh and SO2-poisoned catalysts. Differences in reducibility are related to the formation of quasi-linear Cu-complexes in the SO2-poisoned catalyst formed during heating in H2/He. Heating in H2/He leads to partial desulfurization of the poisoned catalyst. Cooling in H2/He after heating results in more facile formation of Cu-metal clusters in fresh catalyst than in SO2-poisoned.
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| 2. |
- Dahlin, Sandra, et al.
(author)
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Chemical aging of Cu-SSZ-13 SCR catalysts for heavy-duty vehicles –Influence of sulfur dioxide
- 2018
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In: Catalysis Today. - Amsterdam : Elsevier. - 0920-5861 .- 1873-4308. ; 320, s. 72-83
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Journal article (peer-reviewed)abstract
- Selective catalytic reduction of nitrogen oxides is an efficient technique for emission abatement in heavy-dutyvehicles. Cu-SSZ-13 SCR catalysts are more active than vanadium-based catalysts at low temperatures, but aremore sensitive to deactivation by sulfur. Consequently, there is a need to study poisoning by sulfur for thiscatalyst material. This experimental investigation focuses on the effect of sulfur on the low-temperature per-formance of Cu-SSZ-13 SCR catalysts. The effect of sulfur exposure temperature, and the influence of the NO 2 /NO x ratio, are considered and two different regeneration temperatures are compared. In addition, catalystsamples from an engine-aged catalyst are evaluated. The SO 2 exposure temperature is shown to have an im-portant impact on the deactivation of the Cu-SSZ-13 catalyst. The lowest sulfur exposure temperature (220 °C)results in the most severe deactivation, while the highest temperature during sulfur exposure (400 °C) results inthe lowest degree of deactivation. This was found to be related to the amount of sulfur on the catalyst.Additionally, SO 2 exposure was shown to decrease the N 2 O selectivity. The engine-aged catalyst has a decreasedperformance in terms of both decreased activity and increased N 2 O selectivity. For this catalyst, impurities fromfuel and engine-oil can play a role in the deactivation. Different deactivation mechanisms are seen for the lab-and engine-aged catalysts.
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| 3. |
- Dahlin, Sandra, et al.
(author)
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Effect of biofuel- and lube oil-originated sulfur and phosphorus on the performance of Cu-SSZ-13 and V2O5-WO3/TiO2 SCR catalysts
- 2021
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In: Catalysis Today. - : Elsevier B.V.. - 0920-5861 .- 1873-4308. ; 360, s. 326-339
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Journal article (peer-reviewed)abstract
- Two different SCR catalysts, V2O5-WO3/TiO2 and Cu-SSZ-13, were exposed to biodiesel exhausts generated by a diesel burner. The effect of phosphorus and sulfur on the SCR performance of these catalysts was investigated by doping the fuel with P-, S-, or P + S-containing compounds. Elemental analyses showed that both catalysts captured phosphorus while only Cu-SSZ-13 captured sulfur. High molar P/V ratios, up to almost 3, were observed for V2O5-WO3/TiO2, while the highest P/Cu ratios observed were slightly above 1 for the Cu-SSZ-13 catalyst. Although the V2O5-WO3/TiO2 catalyst captured more P than did the Cu-SSZ-13 catalyst, a higher degree of deactivation was observed for the latter, especially at low temperatures. For both catalysts, phosphorus exposure resulted in suppression of the SCR performance over the entire temperature range. Sulfur exposure, on the other hand, resulted in deactivation of the Cu-SSZ-13 catalyst mainly at temperatures below 300-350 °C. The use of an oxidation catalyst upstream of the SCR catalyst during the exhaust-exposure protects the SCR catalyst from phosphorus poisoning by capturing phosphorus. The results in this work will improve the understanding of chemical deactivation of SCR catalysts and aid in developing durable aftertreatment systems.
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| 4. |
- Englund, Johanna, 1988, et al.
(author)
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Deactivation of a Pd/Pt Bimetallic Oxidation Catalyst Used in a Biogas-Powered Euro VI Heavy-Duty Engine Installation
- 2019
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In: Catalysts. - : MDPI. - 2073-4344. ; 9:12
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Journal article (peer-reviewed)abstract
- The reduction of anthropogenic greenhouse gas emissions is crucial to avoid further warming of the planet. We investigated how effluent gases from a biogas powered Euro VI heavy-duty engine impact the performance of a bimetallic (palladium and platinum) oxidation catalyst. Using synthetic gas mixtures, the oxidation of NO, CO, and CH4 before and after exposure to biogas exhaust for 900 h was studied. The catalyst lost most of its activity for methane oxidation, and the activity loss was most severe for the inlet part of the aged catalyst. Here, a clear sintering of Pt and Pd was observed, and higher concentrations of catalyst poisons such as sulfur and phosphorus were detected. The sintering and poisoning resulted in less available active sites and hence lower activity for methane oxidation.
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| 5. |
- Englund, Johanna, 1988, et al.
(author)
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Deactivation of a Vanadium-Based SCR Catalyst Used in a Biogas-Powered Euro VI Heavy-Duty Engine Installation
- 2020
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In: Catalysts. - : MDPI AG. - 2073-4344. ; 10:5
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Journal article (peer-reviewed)abstract
- We have investigated how the exhaust gases from a heavy-duty Euro VI engine, powered with biogas impact a vanadium-based selective catalytic reduction (SCR) catalyst in terms of performance. A full Euro VI emission control system was used and the accumulation of catalyst poisons from the combustion was investigated for the up-stream particulate filter as well as the SCR catalyst. The NO(x)reduction performance in terms of standard, fast and NO2-rich SCR was evaluated before and after exposure to exhaust from a biogas-powered engine for 900 h. The SCR catalyst retains a significant part of its activity towards NO(x)reduction after exposure to biogas exhaust, likely due to capture of catalyst poisons on the up-stream components where the deactivation of the oxidation catalyst is especially profound. At lower temperatures some deactivation of the first part of the SCR catalyst was observed which could be explained by a considerably higher surface V4+/V(5+)ratio for this sample compared to the other samples. The higher value indicates that the reoxidation of V(4+)to V(5+)is partially hindered, blocking the redox cycle for parts of the active sites.
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| 6. |
- Englund, Johanna, 1988
(author)
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Deactivation of after-treatment catalysts for bio-fuelled engines
- 2020
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Doctoral thesis (other academic/artistic)abstract
- To decrease the emissions of anthropogenic CO2 from vehicles one option is to increase the utilization of biobased fuels. However, there are challenges with this transition, one being the mitigation of emissions of the potent greenhouse gas methane, which is the main constituent of biogas. Another relates to the presence of catalyst poisons in biofuels due to a wide variety of raw materials that are used for the production of these fuels. In this thesis, the aim is to investigate how exhausts from biogas and biodiesel impact the emission control system of a heavy-duty vehicle. The catalysts in the emission control system are studied individually and as a system, with commercial biobased fuels and synthetic gas feeds containing catalyst poisons. After exposure to biogas exhaust for 900 h in an engine-bench, the Pd/Pt-Al2O3 oxidation catalyst was found to be severely deactivated in terms of CH4 oxidation activity. A decrease in low-temperature activity for NO oxidation to NO2 was observed, which impacts the performance of the SCR-catalyst down-stream in the system. This loss in activity is explained by the finding of catalyst poisons as well as metal segregation and sintering of the noble metal particles. The V2O5-WO3/TiO2 SCR-catalyst in the engine-bench system remained active for NOx reduction after long-term ageing, however, the decrease in NO2 formation over the oxidation catalyst at low temperatures could cause an increase in NOx emissions even if the SCR catalyst itself is still active. Except for the vanadium-based SCR catalyst also a Cu-CHA catalyst was studied. Both types of SCR catalysts were found to be sensitive to phosphorus poisoning and the Cu-CHA catalyst was also found to be sensitive to sulfur. From results obtained we propose that the SO2 exposure leads to the formation of Cu-bisulfate species that reduce the amount of copper sites available for NOx reduction in the Cu-CHA SCR catalyst. The degree of deactivation is also dependent on the reaction condition where the standard SCR reaction is more impacted than the fast SCR reaction.
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| 7. |
- Englund, Johanna, 1988
(author)
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Deactivation of SCR catalysts - Impact of sulfur and the use of biofuels
- 2018
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Licentiate thesis (other academic/artistic)abstract
- In a near future, limits on CO2 emissions from vehicles will be introduced, which requires development of more fuel-efficient engines and most likely a transition towards the use of more biofuels. With the implementation of biofuels several issues could arise, one being the lack of fuel standards for these new type of fuels, leading to higher concentrations of catalyst poisons compared to conventional fossil fuels. This work specifically focuses on catalyst poisoning originating from biofuels and is based on two papers. The aim of the work presented in paper I is to study the influence of SO2 on the low-temperature performance of a Cu-SSZ-13 SCR (selective catalytic reduction) catalyst. In particular the sulfur exposure temperature and the influence of the NO2/NOx ratio are considered, and two different regeneration temperatures are investigated. The results show that the temperature at which the Cu-SSZ-13 catalyst is exposed to SO2 is a critical parameter. The lowest exposure temperature (220°C) resulted in the most pronounced deactivation, while the highest exposure temperature (400°C) caused the lowest degree of deactivation of the catalyst. It was also shown that the exposure to SO2 resulted in decreased N2O selectivity. Engine-aging of the Cu-SSZ-13 catalyst resulted in decreased SCR activity and increased selectivity towards N2O formation, which most likely is caused by impurities from the fuel and engine-oil. In paper II, the influence of the fuel on the functionality of a commercial vanadia-based SCR catalyst after extended field-operation is investigated. The NH3-SCR activity, NH3-oxidation activity, NH3 adsorption capacity, specific surface area and surface composition were measured before and after field-operation in two heavy-duty Euro V vehicles fuelled with fatty acid methyl ester (FAME) and hydrotreated vegetable oil (HVO), respectively. For the catalyst samples taken from the vehicle fuelled with FAME, the NH3-SCR activity, NH3-oxidation activity and NH3 adsorption capacity were significantly lower compared to the fresh sample and the samples taken from the vehicle fuelled with HVO. This is likely due to accumulation of catalyst poisons that originates from the FAME fuel that cause blocking of the active sites on the vanadia-based catalyst. The studies of single poison compounds in lab-scale experiments are important for the understanding of catalyst deactivation mechanisms, however, there are many more parameters that dictates the deactivation in a vehicle. This can be seen from the engine-aged samples in both paper I and II where a single poison cannot fully explain the observed deactivation.
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| 8. |
- Englund, Johanna, 1988, et al.
(author)
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Impact of palladium distribution in alumina on low-temperature oxidation of carbon monoxide
- 2016
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Conference paper (other academic/artistic)abstract
- When emission standards for vehicles are becoming more stringent, catalysts that efficiently oxidize CO and HC (hydrocarbons) are a necessity. One of the important aspects here is to improve efficiency at low temperatures. This is emphasized by the change in technology towards more fuel-efficient engines which results in colder emissions and the need for reducing cold-start emissions [1]. Low-temperature oxidation can be enhanced using different strategies [2]. New materials and combinations of materials could be one solution and in that context the distribution of the active phase in the support material is crucial [3]. The distribution of the active phase will influence mass and heat transfer and thereby control the conversion of the reactants. Previously, it has been shown that heterogeneous distribution of the active phase (Pt) in the support material can improve the oxidation of CO at low temperatures [3]. The idea was that concentrate the active phase locally in the support material would result in a better utilization of generated reaction heat leading to higher temperatures of the active sites and, therefore, promote higher activity. The study showed an increase in activity for the samples with heterogeneous distribution of the active phase but it was also concluded that the enhancement in activity most likely arises from mass transfer effects.
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