| 1. |
- 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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| 2. |
- Di, Mengqiao, 1994, et al.
(author)
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Chasing PtO x species in ceria supported platinum during CO oxidation extinction with correlative operando spectroscopic techniques
- 2022
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In: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 409, s. 1-11
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Journal article (peer-reviewed)abstract
- Industrially relevant, highly dispersed, Pt/ceria and reference Pt/alumina catalysts with narrow Pt particle size distributions have been prepared, characterised ex situ and studied for CO oxidation by operando infrared and X-ray absorption spectroscopy. At high CO conversions, spectator CO ad-species on ionic platinum are observed while the CO oxidation proceeds on Pt particles in a high oxidation state exhibiting significant Pt[sbnd]O coordination. During the protracted catalytic extinction, the CO coverage builds up gradually while the Pt oxidation state and Pt[sbnd]O coordination remain high because of interactions with ceria. The observed CO oxidation at high CO coverage is suggested to involve sites at the platinum-ceria boundary that cannot be CO self-poisoned. This behaviour is in stark contrast to that of Pt/alumina, which shows removal of platinum oxides formed during CO oxidation and the classical drop in catalytic activity caused by rapid CO self-poisoning when reaching a critical temperature.
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| 3. |
- Shwan, Soran, 1984, et al.
(author)
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Inside front cover
- 2014
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In: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 4:9, s. 2688-2688
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Journal article (peer-reviewed)
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| 4. |
- Wang, Xueting, 1991, et al.
(author)
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Methanol Desorption From Cu-ZSM-5 Studied by In Situ Infrared Spectroscopy and First-Principles Calculations
- 2017
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:49, s. 27389-27398
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Journal article (peer-reviewed)abstract
- The dynamic interaction of methanol and its derivatives with Cu-exchanged ZSM- 5 during methanol temperature programmed desorption from 30 to 450 ◦C has been investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy and first-principles calculations. The results emphasize that defects in the framework structure of the zeolite and Brønsted acid sites constitute ion-exchange sites for Cu ions. The Cu sites introduced in ZSM-5 actively interact with methanol adsorbed at moderate temperature, i.e. below 250◦C, and take roles in further oxidation of the adsorbed species to formate and CO. Moreover, spectra recorded at higher temperatures, i.e. above 300◦C, after adsorption of methanol show strong interaction between methoxy groups and the zeolite framework, suggesting that under mild conditions proton extraction for methanol production during direct partial oxidation of methane to methanol over Cu-ZSM-5 is necessary.
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| 5. |
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| 6. |
- Bounechada, Djamela, 1984, et al.
(author)
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Vibrational Study of SOx Adsorption on Pt/SiO2
- 2014
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:51, s. 29713-29723
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Journal article (peer-reviewed)abstract
- The formation of ad-SOx species on Pt/SiO2 upon exposure to SO2 in concentrations rang- ing from 10 to 50 ppm at between 200 and 400◦C has been studied by in situ diffuse reflectance infrared Fourier transformed spectroscopy. In parallel, first-principles calculations have been carried out to consolidate the experimental interpretations. It was found that sulfate species form on the silica surface with a concomitant removal/ rearrangement of silanol groups. For- mation of ad-SOx species occurs only after SO2 oxidation to SO3 on the platinum surface. Thus SO2 oxidation to SO3 is the first step in the SOx adsorption process, followed by spillover of SO3 to the oxide and, finally, the formation of sulfate species on the hydroxyl positions on the oxide. The sulfate formation is influenced by both temperature and SO2 concentration. Furthermore, exposure to hydrogen is shown to be sufficiently efficient as to remove ad-SOx species from the silica surface.
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| 7. |
- 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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| 8. |
- Wallin, Mikaela, 1975, et al.
(author)
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Vibrational Analysis of H2 and D2 Adsorption on Pt/SiO2
- 2005
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 109:19, s. 9581-9588
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Journal article (peer-reviewed)abstract
- Vibrational properties of surface species formed upon H2 and D2 exposure of silica supported platinum particles have been investigated with in situ diffuse reflection infrared Fourier transform spectroscopy. Experiments have been performed at 50-250 degrees C, using different platinum loading of the samples in the absence and presence of oxygen. In addition, electronic structure calculations and vibrational analysis have been performed within the density functional theory for H adsorption on a silica cluster, (HO)(3)SiOSi(OH)(3). The spectroscopy experiments showed reversible formation of isolated OH and OD groups on the silica surface when the samples were exposed to H2 and D2, respectively. In addition to the absorption peak corresponding to isolated OH and OD groups, an intense broad band was observed around 3270 cm(-1) (2500 cm(-1)) during H2 (D2) exposure. Supported by the calculations, this band was assigned to perturbed OH groups on the silica surface. The surface coverage of new OH groups was found to correlate to the platinum loading in the samples, indicating that the new silanol groups were formed in the vicinity of the Pt particles. In the investigated temperature interval, the formation rate of CH groups was not found to be temperature dependent.
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| 9. |
- Ek, Martin, 1984, et al.
(author)
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Redox dynamics of 2D crystalline vanadium oxide phases on high-index anatase facets
- 2023
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In: Nanoscale. - 2040-3372 .- 2040-3364. ; 15:21, s. 9503-9509
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Journal article (peer-reviewed)abstract
- Vanadium oxides exist in a multitude of phases with varying structure and stoichiometry. This abundance of phases can be extended through the use of other oxides as supports, and through redox treatments. However, the combined effects of different supports and redox treatments can be difficult to identify, particularly when present as different terminating facets on nanoparticles. Here, we examine structural dynamics of 2D vanadium oxides supported on anatase TiO2 nanoparticles, correlated with changes in oxidation state, using in situ transmission electron microscopy imaging and electron energy loss spectroscopy. As the average oxidation state is reduced below V(iv), an ordered cubic V(ii) phase is observed exclusively at the high-index {10l} facets of the support. This local accommodation of highly reduced states is necessary for explaining the observed range of average oxidation states. In turn, the findings show that oxidation states extending from V(v)-V(iv) to V(ii) can be simultaneously stabilized by different supporting oxide surfaces during exposure to atmospheres with controlled redox potential.
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| 10. |
- 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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