| 1. |
- Auvray, Xavier, 1986, et al.
(författare)
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The effect gas composition during thermal aging on the dispersion and NO oxidation activity over Pt/Al2O3 catalysts
- 2013
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 129, s. 517-527
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Tidskriftsartikel (refereegranskat)abstract
- The aging of a model 1 wt.% Pt/Al2O3 catalyst was performed stepwise under different reactive atmosphere to study the evolution of metal dispersion and NO oxidation activity. After each aging step the dispersion was evaluated by CO chemisorptions and the activity of the catalyst for NO oxidation was measured using 500 ppm NO and 8%O-2 diluted in Ar. After a degreening step at 500 degrees C, aging was performed at 600, 700,800 and 900 degrees C. Five wash-coated cordierite monoliths were aged in Ar, 10% O-2, 1% H-2 30 ppm SO2 and 30 ppm SO2 + 10% O-2, respectively. The general trend showed a linear decrease in dispersion when increasing the aging temperature for the lower aging temperatures and for the highest ones the dispersion levels off. When the platinum dispersion decreased the NO oxidation activity increased, due to that the reaction is structure sensitive. H-2 seemed to hinder sintering at low aging temperature. Interestingly, after aging in 10% oxygen at 600 degrees C the NO oxidation activity was significantly higher compared to the Ar aged sample, although the dispersions were similar. Aging in oxygen at higher temperatures resulted in a decrease of dispersion and a slightly decreasing NO oxidation activity. Moreover lower dispersion limit was reached with oxygen aging. Aging in SO2 provoked a severe dispersion drop at low aging temperature meanwhile the activity increased only moderately. However, activity kept increasing with further treatments at higher temperature. The combination of O-2 and SO2 enabled to decrease rapidly the dispersion and to greatly enhance the catalytic NO oxidation activity after the first aging step at only 600 degrees C. The best overall conversion was obtained for the catalyst treated with this mixture after aging at 800 degrees C. A 22-h aging at 250 degrees C in a mixture containing 500 ppm NO, 10% O-2 and 30 ppm SO2 led to a significant decrease of Pt dispersion, which shows the ability of SO2 to promote platinum sintering already 250 degrees C. The low temperature sintering was confirmed with STEM measurements. Several larger particles were observed, but also many small particles remained. Thus the SO2 + O-2 induced low temperature sintering results in a large variation of particle sizes. This treatment resulted in an increase of the maximum NO conversion (after reduction of the sample) from 45% to 76%. The different aging experiments show that it is beneficial to add SO2 during aging and the reason is the increased particle size, but also a clear chemical effect was observed.
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| 2. |
- Adermark, Louise, 1974, et al.
(författare)
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Implications for glycine receptors and astrocytes in ethanol-induced elevation of dopamine levels in the nucleus accumbens.
- 2011
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Ingår i: Addiction biology. - : Wiley. - 1369-1600 .- 1355-6215. ; 16:1, s. 43-54
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Tidskriftsartikel (refereegranskat)abstract
- ABSTRACT Elevated dopamine levels are believed to contribute to the rewarding sensation of ethanol (EtOH), and previous research has shown that strychnine-sensitive glycine receptors in the nucleus accumbens (nAc) are involved in regulating dopamine release and in mediating the reinforcing effects of EtOH. Furthermore, the osmoregulator taurine, which is released from astrocytes treated with EtOH, can act as an endogenous ligand for the glycine receptor, and increase extracellular dopamine levels. The aim of this study was to address if EtOH-induced swelling of astrocytes could contribute to elevated dopamine levels by increasing the extracellular concentration of taurine. Cell swelling was estimated by optical sectioning of fluorescently labeled astrocytes in primary cultures from rat, and showed that EtOH (25-150 mM) increased astrocyte cell volumes in a concentration- and ion-dependent manner. The EtOH-induced cell swelling was inhibited in cultures treated with the Na(+)/K(+)/2Cl(-) cotransporter blocker furosemide (1 mM), Na(+)/K(+)-ATPase inhibitor ouabain (0.1 mM), potassium channel inhibitor BaCl(2) (50 microM) and in cultures containing low extracellular sodium concentration (3 mM). In vivo microdialysis performed in the nAc of awake and freely moving rats showed that local treatment with EtOH enhanced the concentrations of dopamine and taurine in the microdialysate, while glycine and beta-alanine levels were not significantly modulated. EtOH-induced dopamine release was antagonized by local treatment with the glycine receptor antagonist strychnine (20 microM) or furosemide (100 microM or 1 mM). Furosemide also prevented EtOH-induced taurine release in the nAc. In conclusion, our data suggest that extracellular concentrations of dopamine and taurine are interconnected and that swelling of astrocytes contributes to the acute rewarding sensation of EtOH.
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| 3. |
- Andonova, Stanislava, 1977, et al.
(författare)
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Chemical deactivation by phosphorous under lean hydrothermal conditions over Cu/BEA NH3-SCR catalysts
- 2014
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 147, s. 251-263
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Tidskriftsartikel (refereegranskat)abstract
- To obtain a better understanding of the deactivation of SCR catalysts that may be encountered due to the presence of P-containing impurities in diesel exhausts, the effects induced by P over Cu/BEA NH3-SCR catalysts were studied as functions of the temperature of poisoning and P concentration in the feed. Cu/BEA catalysts with different Cu loadings (4 and 1.3 wt% Cu) were exposed to P by controlled evaporation of H3PO4 in the presence of 8% O2 and 5% H2O at 573 and 773 K. The reaction studies were performed by NH3-storage/TPD, NH3/NO oxidation and standard NH3-SCR. In addition, a combination of several characterisation techniques (ICP–AES, BET surface area, pore size distribution, H2-TPR and XPS) was applied to provide useful information regarding the mechanism of P deactivation. Pore condensation of H3PO4 in combination with pore blocking was observed. However, the measured overall deactivation was found to occur mostly by chemical deactivation reducing the number of the active Cu species and hence deteriorating the redox properties of the Cu/BEA catalysts. The process of P accumulation on the surface preferentially occurs on the “over exchanged” Cu active sites with the formation of phosphate species. This is likely the reason for the more severe deactivation of the 4% Cu/BEA compared to 1.3% Cu/BEA. Further, the higher NOx reduction performance at 773 K of the P-poisoned Cu/BEA catalysts was found to originate from the lower selectivity towards NH3 oxidation, which occurs predominately on the “over-exchanged” sites.
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| 4. |
- Andonova, Stanislava, 1977, et al.
(författare)
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Enhanced Low Temperature NOx Reduction Performance Over Bimetallic Pt/Rh-BaO Lean NOx Trap Catalysts
- 2013
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 56:1-8, s. 68-74
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Tidskriftsartikel (refereegranskat)abstract
- The overall NSR operation was tested over a bimetallic Pt/Rh-BaO lean NO (x) trap (LNT) catalyst in the range of 473-673 K with simulated diesel exhausts and compared to monometallic 1 wt% Pt/BaO/gamma-Al2O3 and 0.5 wt% Rh/BaO/gamma-Al2O3 samples. The results showed the beneficial effect of the simultaneous presence of 0.5 wt% Pt and 0.25 wt% Rh on the catalytic performance under lean-burn conditions at low temperatures. It was observed that both Pt/BaO/gamma-Al2O3 and Rh/BaO/gamma-Al2O3, which both were mildly aged, have limited NO (x) reduction capacity at 473 K. However, combining Pt and Rh in the NO (x) storage catalyst assisted the NO (x) reduction process to occur at lower temperatures (473 K). One possible reason could be that the combined Pt and Rh sample was more resistant to aging. In addition, the NO2-TPD data showed that the presence of Rh into the Pt/BaO/gamma-Al2O3 system has a considerable effect on the spill-over process of NO (x) , accelerating the release of NO (x) at lower temperatures. These results were in a good agreement with the observed higher rate of oxygen release of the bimetallic Pt/Rh catalyst, leaving a significant number of noble metal sites available for adsorption at lower temperatures than that of the monometallic Pt sample. The superior NSR performance of the bimetallic Pt/Rh/BaO/gamma-Al2O3 catalyst under lean-burn conditions suggested the existence of synergetic promotion effect between the Pt and Rh components, increasing the NO (x) reduction efficiency in comparison with that of the monometallic Pt and Rh-BaO LNT catalysts.
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| 5. |
- Andonova, Stanislava, 1977, et al.
(författare)
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Mechanistic investigations of the promoting role of Rh on the NSR performance of NOx storage BaO-based catalysts
- 2013
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 132, s. 266-281
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Tidskriftsartikel (refereegranskat)abstract
- To determine the promoting effect of Rh on the overall NOx storage and reduction (NSR) performance, the studies in the current work were directed toward investigating the storage and release ability over Rh NOx storage BaO-based catalysts compared to Pt. In terms of the metal surface dispersion and the ability of the noble metals to release oxygen at lower temperatures, the synthesized catalysts were characterized by means of dynamic CO chemisorption (RT) and N2O dissociation (RI - 773 K). The NOx storage capacity and the thermal stability of the NOx adsorbed species formed on the surface were analyzed via NOx storage tests and temperature programmed desorption (TPD) without and in the presence of CO2 and H2O. In addition, experiments with lean and rich cycling were conducted at 473,573 and 673 K. The results from the N2O dissociation experiments showed the superior ability of Rh/Al and Rh/Ba/Al catalysts compared to Pt toward O-2 release from the catalytic surface at lower temperatures. In this work, we show that the presence of Rh into the BaO/gamma-Al2O3 system has a considerable effect on the spill-over process of NOx to the precious metal, controlling the subsequent desorption of NOx to occur at lower temperatures in comparison with that of the Pt catalysts. It is suggested a mechanism of NOx desorption where the lower temperature of O-2 release from the surface of Rh catalysts could leave a significant number of noble metal sites accessible for adsorption. Thus this could facilitate the rate of spill-over of NOx from the storage site (the surface sites on gamma-Al2O3 and those on BaO) to the noble metal and their desorption at lower temperatures. The limited NOx storage ability of the Rh-based BaO/gamma-Al2O3 catalysts under lean-burn conditions was found to originate from both low NO oxidation activity and NOx reduction activity, while the main limiting factor for the low NSR performance of the Pt-based catalysts was the limited regeneration ability during rich period.
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| 6. |
- Auvray, Xavier, 1986, et al.
(författare)
-
Effect of enhanced support acidity on the sulfate storage and the activity of Pt/γ-Al2O3 for no oxidation and propylene oxidation
- 2014
-
Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 144:1, s. 22-31
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Tidskriftsartikel (refereegranskat)abstract
- NO oxidation and propylene oxidation were studied on standard and acidity-enhanced Pt/Al 2 O 3 catalyst. Deactivation by platinum oxide formation was suppressed by the presence of chlorine and sulfates. After a long SO 2 exposure, the activity of modified catalysts was higher than the standard catalyst. The aged chlorinated sample showed the best propylene oxidation activity while the sulfated one exhibited the best NO conversion. © 2013 Springer Science+Business Media New York.
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| 7. |
- Auvray, Xavier, 1986, et al.
(författare)
-
Enhancement of NO and C3H6 oxidation by SO2 treatment over Pt/Al2O3
- 2013
-
Ingår i: 23rd Meeting of the North American Catalysis Society, Louisville, KY, June 2013.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Oxidation catalyst is used in automotive exhaust treatment to convert CO and hydrocarbons into CO2 and water. They also have the specific function of converting NO into NO2 in Diesel vehicles, which increases the efficiency of NOx-removal system and participates in the particle filter regeneration. Automotive catalysts are affected by thermal treatments and gas composition. SO2 is one of the undesirable compounds of exhaust gases that is able to store on the catalyst [1] and hinder the reaction. Despite its low concentration, SO2 affects significantly the catalyst. Ageing in SO2-containing atmosphere has shown to promote platinum migration and increase the ability of Pt/Al2O3 catalysts to oxidize NO in dry conditions [2]. In the present work, model catalysts were aged in presence of SO2 at 250 °C and tested for NO and C3H6 oxidation in wet conditions. Various reductive treatments were performed after ageing in order to shed a light on the stability and impact on activity of the different types of adsorbed sulfur species. The hysteresis phenomenon observed for both reactions was also affected by the presence of surface sulfur.The performance of a typical oxidation catalyst was improved by pretreatment in presence of SO2 and subsequent elimination of the less stable stored sulfur species. Further activity was gained during the cooling for both NO and C3H6 oxidation after complete removal of sulfur.
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| 8. |
- Auvray, Xavier, 1986, et al.
(författare)
-
Enhancement of NO and C3H6 oxidation by SO2 treatment over Pt/Al2O3
- 2013
-
Ingår i: Energirelaterad fordonsforskning 2013, Örebro, April 2013.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The oxidation of NO and C3H6 over a 1wt% Pt/Al2O3 catalyst was studied. Ageing of the catalyst at 250 °C for 22 h with a gas flow containing 30 ppm SO2 decreased the dispersion and increased the catalytic activity for the two reactions. Two types of sulfur species were formed during ageing, the less stable of which have to be eliminated to recover high activity. The most stable species, probably sulfates stored on the support, affect the conversion during extinction only.
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| 9. |
- Auvray, Xavier, 1986, et al.
(författare)
-
Local ammonia storage and ammonia inhibition in a monolithic copper-beta zeolite SCR catalyst
- 2012
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 126, s. 144-152
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Tidskriftsartikel (refereegranskat)abstract
- Selective catalytic reduction of NO with NH3 was studied on a Cu-beta zeolite catalyst, with specific focus on the distributed NH3 capacity utilization and inhibition. In addition, several other relevant catalyst parameter distributions were quantified including the SCR zone, or catalyst region where SCR occurs, and NO and NH3 oxidation. We show that the full NH3 capacity (100% coverage) is used within the SCR zone for a range of temperatures. By corollary, unused NH3 capacity exists downstream of the SCR zone. Consequently, the unused capacity relative to the total capacity is indicative of the portion of the catalyst unused for SCR. Dynamic NH3 inhibition distributions, which create local transient conversion inflections, are measured. Dynamic inhibition is observed where the gas phase NH3 and NO concentrations are high, driving rapid NH3 coverage buildup and SCR. Accordingly, we observe dynamic inhibition at low temperatures and in hydrothermally aged states, but predict its existence very near the catalyst front in higher conversion conditions where we did not specifically monitor its impact. While this paper addresses some general distributed SCR performance parameters including Oxidation and SCR zone, our major new contributions are associated with the NH3 capacity saturation within the SCR zone and dynamic inhibition distributions and the associated observations. These new insights are relevant to developing accurate models, designs and control strategies for automotive SCR catalyst applications.
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| 10. |
- Auvray, Xavier, 1986, et al.
(författare)
-
Sulfur Dioxide Exposure: A Way To Improve the Oxidation Catalyst Performance
- 2013
-
Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 52:41, s. 14556-14566
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of nitric oxide and propylene was studied over a model alumina-supported platinum catalyst. Two treatments (22 h at 250 degrees C and 2 h at 800 degrees C) involving sulfur dioxide were performed in order to understand the effect of SO2 aging. The role and stability of sulfur species stored during aging were investigated by the reduction of sulfated samples at 500 degrees C and temperature-programmed reduction (TPR) up to 800 degrees C. The low activity obtained after aging without reduction revealed the poisoning effect of surface sulfur species. The reduction at 500 degrees C released half of the surface species, which increased the catalytic activity for both NO and C3H6 oxidation. The TPR removed the most stable sulfur species and improved the activity during cooling. The catalyst aged in SO2 at high temperature showed the greatest activity for both reactions because of SO2 exposure and low sulfur storage.
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| 11. |
- Auvray, Xavier, 1986, et al.
(författare)
-
The effect of gas composition during thermal aging on the dispersion and NO oxidation activity over Pt/Al2O3 catalyst
- 2012
-
Ingår i: CapoC 9, August 2012, Brussels, Belgium.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The effect of aging atmosphere (Ar, H2, O2, SO2, SO2+O2) during thermal aging of Pt/Al2O3 model diesel oxidation catalysts was studied. More specifically, the impact of the aging on the NO oxidation activity and platinum dispersion was investigated. Thermal aging caused a decrease in dispersion and an increase in NO oxidation performance. However, the aging behavior was strongly correlated with the nature of the ageing atmosphere. Catalysts with similar dispersion could have very different NO oxidation activity, depending on which atmosphere that they were aged with.
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| 12. |
- Doronkin, D. E., et al.
(författare)
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Study of the "Fast SCR"-like mechanism of H2-assisted SCR of NOx with ammonia over Ag/Al2O3
- 2012
-
Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 113, s. 228-236
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that Ag/Al2O3 is a unique catalytic system for H-2-assisted selective catalytic reduction of NOx by NH3 (NH3-SCR) with both Ag and alumina being necessary components of the catalyst. The ability of Ag/Al2O3 and pure Al2O3 to catalyse SCR of mixtures of NO and NO2 by ammonia is demonstrated, the surface species occurring discussed, and a "Fast SCR"-like mechanism of the process is proposed. The possibility of catalyst surface blocking by adsorbed NOx and the influence of hydrogen on desorption of NOx were evaluated by FTIR and OFT calculations.
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| 13. |
- Fathali, A., et al.
(författare)
-
A comparison of fuel-cut ageing during retardation and fuel-cut during acceleration
- 2014
-
Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 1
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of various fuel-cut agings, on a Volvo Cars 4-cylinder gasoline engine, with bimetallic three-way catalysts (TWCs) was examined. Deactivation during retardation fuel-cut (low load) and acceleration fuel-cut (high load, e.g. gearshift or traction control) was compared to aging at =1. Three-way catalysts were aged on an engine bench comparing two fuel-cut strategies and their impact on of the life and performance of the catalysts. In greater detail, the catalytic activity, stability and selectivity were studied. Furthermore, the catalysts were thoroughly analyzed using light-off and oxygen storage capacity measurements. The emission conversion as a function of various lambda values and loads was also determined. Fresh and 40-hour aged samples showed that the acceleration fuel-cut was the strategy that had the highest contribution towards the total deactivation of the catalyst system. Also, the retardation fuel-cut was found to be detrimental to the catalyst system but not to the same extent as an acceleration fuel-cut. During the aging procedure, exotherms were observed at the fuel-cut and the intensity of these exotherms was increasing with the length of aging time. The growing exotherms could be explained by the decomposition of HC into C and H2 and their subsequent oxidation at lean conditions. Also, the fuel-cut-off temperature measurements demonstrated that the magnitude of those exotherms was related to the total number as opposed to the total length of the fuel-cut. Copyright © 2014 SAE International.
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| 14. |
- Fathali, Anna, 1981, et al.
(författare)
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Hydrothermal Aging-Induced Changes in Washcoats of Commercial Three-Way Catalysts
- 2013
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 56:1-8, s. 323-328
-
Tidskriftsartikel (refereegranskat)abstract
- In order to quantify hydrothermal aging effects on the mono- and bi-metallic Pd and Rh supported on cerium-zirconium promoted alumina commercial three-way catalysts (TWCs), the catalysts were tested both fresh and after accelerated hydrothermal aging. The catalytic tests showed clear deactivation of the aged samples and influence on TWC's property, such as: light-off temperature, specific surface area (BET), dispersion of noble metals, oxygen storage capacity, oxygen storage capacity complete and labile oxygen storage capacity. Water inhibition have been investigated and confirmed for the performance of NOx reduction of the fresh catalyst. X-ray photoelectron spectroscopy was used to study changes in the oxidation state of the Pd and Rh present in the washcoat of the catalyst, before and after hydrothermal aging. Element maps by SEM-EDX analysis was perform in order to characterize the catalysts morphology, the surface's composition and element distribution.
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| 15. |
- Li, J. H., et al.
(författare)
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Characterization of Active Species in Cu-Beta Zeolite by Temperature-Programmed Reduction Mass Spectrometry (TPR-MS)
- 2013
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 56:1-8, s. 201-204
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Tidskriftsartikel (refereegranskat)abstract
- The number and type of copper species present in an under-exchanged Cu-Beta zeolite catalyst were characterized using temperature-programmed reduction mass spectrometry (TPR-MS). Both H-2 consumption and H2O evolution were tracked, yielding additional insights into the nature of Cu species. Prior to the TPR-MS tests, catalyst samples were subjected to various high- temperature aging treatments in the presence of O-2 in He, in order to assist with interrogating and resolving different types of sites. Absence of reducible species in the precursor material was confirmed by subjecting the H-form of the same zeolite to the TPR. Upon aging at temperatures below 700 A degrees C, the TPR pattern showed several distinct peaks of different intensities. Aging at 800 A degrees C led to shifting and broadening of these H-2 consumption peaks, as well as to some reduction of the integral amount of the reducible sites. The 900 A degrees C exposure resulted in a drastic change of the TPR pattern, with several new well-resolved H-2 consumption peaks, indicative of drastic changes in the catalyst structure. The integral amount of H-2 consumed quantitatively matched the amount of Cu species present in the catalyst, assuming the stoichiometry. The combination of experimental findings in this work lends support to a hypothesis that different TPR peaks are indicative of different types of sites rather than of step-wise reduction of copper species.
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| 16. |
- Lindholm, Anna Maria, 1977, et al.
(författare)
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Reduction of NOx over a combined NSR and SCR system
- 2010
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 98:3-4, s. 112-121
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Tidskriftsartikel (refereegranskat)abstract
- Flow reactor experiments are performed over a model Pt/Ba/Al catalyst, an Fe-beta sample, and over a combined system where the Pt/Ba/Al catalyst is placed upstream the Fe-beta sample. The combined system show a superior NOx removal efficiency and a lower ammonia slip compared to the single Pt/Ba/Al catalyst at all temperatures examined. Ammonia, formed during the rich period over the Pt/Ba/Al, is stored in the SCR catalyst and consumed in the following lean period which results in a decrease of the NH3 slip and an increase of the NOx removal efficiency. The optimum temperature for NOx removal of the combined system is 300 degrees C; at this temperature a remarkably high NOx removal efficiency of 99.5% is achieved. The SCR catalyst exhibit a high ammonia adsorption capacity at 200 degrees C which results in a very low NH3 yield (3%) and a high N-2 yield (85%) for the combined NSR and SCR system. There is a benefit when NO2 is present in the feed at low temperatures. The NOx removal efficiency of the combined system increases due to the increase in the amount of NOx stored over the Pt/Ba/Al sample. Furthermore, the amount of NOx removed over the combined system is influenced by the amount of hydrogen in the rich periods. A higher hydrogen concentration enhances the NOx removal efficiency at lower temperatures. At higher temperatures an optimum hydrogen concentration exists due to ammonia inhibition of the SCR reaction when an excessively high H-2 concentration is used. (C) 2010 Elsevier B.V. All rights reserved.
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| 17. |
- Lundström, Andreas, 1980, et al.
(författare)
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Urea decomposition and HNCO hydrolysis studied over titanium dioxide, Fe-Beta and gamma-Alumina
- 2011
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 106:3-4, s. 273-279
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Tidskriftsartikel (refereegranskat)abstract
- The catalytic effect of titanium dioxide, Fe-Beta, gamma-Alumina, on the thermal decomposition of urea and hydrolysis of HNCO, was investigated using differential scanning calorimetry (DSC) and mass spectrometry (MS). The catalytic materials were coated on cordierite substrates and a pure cordierite sample was also used for comparison. The urea was administered by impregnating the monoliths with an urea/water solution. The experiments were performed using a constant heating rate of 10 K/min and over a temperature range of 25-500 degrees C. A sweep gas flow rate of 80 mL/min of either dry or humid Ar was used. The results show that TiO(2) is the best hydrolysis catalyst. Fe-Beta showed a very large ammonia production, due to selective adsorption of urea during the impregnation of the monolith in the urea solution. One experiment with lower flow, higher urea loading and increased ramp speed conducted in dry Ar over TiO(2) showed a large formation of biproducts. This experiment was repeated in the presence of water and this decreased the formation of CYA and biuret significantly. The reason for this is the effective hydrolysis of the HNCO over titania, which hindered the bi-product formation.
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| 18. |
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| 19. |
- Mihai, Oana, 1975, et al.
(författare)
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DME, propane and CO: The oxidation, steam reforming and WGS over Pt/Al2O3. The effect of aging and presence of water
- 2014
-
Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 160-161:1, s. 480-491
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Tidskriftsartikel (refereegranskat)abstract
- The effect of aging in two environments (Ar at 800°C and SO2+NO+O2+H2O at 250°C) on oxidation/steam reforming reactions using dimethyl ether (DME), propane and CO were investigated on Pt/Al2O3 catalysts. Platinum dispersion as well as the changes in Pt-particles sizes were examined. The BET surface area of aged catalysts decreased compared to the fresh (degreened) sample, indicating that aging in inert gas may collapse some pores in alumina and for aging in sulfur atmosphere it may block some pores of the catalysts. Using SEM/EDX, higher sulfur amount was found in the inlet position of the aged sulfur monolith and it decreased linearly with the direction of the flow along the monolith length. The effect of water was also studied and it was found that propane and DME oxidation is negatively influenced by the presence of water, while for CO an increased activity was found. Thermal aging of the Pt/Al2O3 catalyst resulted in quite small deactivation for the examined reactions. The dispersion after the sulfur aging, and subsequent H2 reduction, was the same as after the thermal aging at 800°C, but interestingly the activity is significantly different. After the sulfur aging and hydrogen regeneration, the DME and C3H8 oxidation is promoted, while CO oxidations are slightly inhibited in the presence of water. The effect of the sulfur aging had a minor effect on DME-SR, while it completely deactivated steam reforming for propane. For the WGS reaction, the sulfur aging resulted in an overall decreased activity and in addition the conversion went through a maximum. We suggest that residues of sulfur on the alumina inhibit the water activation in the WGS reaction.
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| 20. |
- Mihai, Oana, 1975, et al.
(författare)
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The effect of Cu-loading on different reactions involved in NH3-SCR over Cu-BEA catalysts
- 2014
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 311, s. 170-181
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigate the effect of varying copper loading in Cu-BEA on different reactions involved in the SCR mechanism. The catalysts were characterized by BET, ICP-AES, and UV-Vis. Enlarged ammonia storage was observed when increasing the copper loading mainly owing to loosely bonded NH3, but for over-exchanged samples, a new high-temperature shoulder was also observed. The N2O production significantly grew with increasing copper loading. In addition, the reaction rates of NO oxidation and NH3 oxidation per Cu site were higher on the high-loaded copper samples compared to those with lower loading. However, the opposite results were found for NH3 SCR, but differences were small for this reaction. Ammonium nitrate formation and decomposition were examined during a variety of temperature-programmed desorption (TPD) experiments, and three regions related to the presence of acid sites and low- versus high-loaded copper sites were observed. When dosing NO2 before NH3, ammonium nitrate species were formed but in lower amounts than if NH3 and NO2 were dosed simultaneously.
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| 21. |
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| 22. |
- Mihai, Oana, 1975, et al.
(författare)
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The Effect of NO2/NOx Feed Ratio on the NH3-SCR System Over Cu–Zeolites with Varying Copper Loading
- 2014
-
Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 144:1, s. 70-80
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Tidskriftsartikel (refereegranskat)abstract
- In this study we examine the NO/NO2–NH3-SCR system over Cu–BEA with varying Cu loading. Significantly higher selective catalytic reduction (SCR) activity is observed at low temperature on highly loaded copper samples, whereas the reverse trend is noticed at high temperature. The N2O formation is substantially increased over “over-exchanged” Cu sites, where Cu co-ordinate to one Al and charge-balanced with one OH-group. This is also the case for NO2 reaction with NH3 to produce NO. Using transient experiments the formation/decomposition of ammonium nitrate species are examined. The decomposition depends on the temperature, the sequence of the feed as well as the type of copper species present.
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| 23. |
- Nedyalkova, Radka, 1976, et al.
(författare)
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Experimental evidence of the mechanism behind NH3 overconsumption during SCR over Fe-zeolites
- 2013
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 299, s. 101-108
-
Tidskriftsartikel (refereegranskat)abstract
- Isotope labeled (NO)-N-15 was used to investigate the mechanism of the unusual overconsumption of NH3 during standard SCR over Fe-zeolite, under conditions during which NH3 oxidation with O-2 alone (without NO) was unfavorable. When the Fe-BEA catalyst was exposed to the (NO)-N-15 + (NH3)-N-14 + O-2 gas mixture at 250 and 300 degrees C, the resulting products included (NO)-N-14, a product of (NH3)-N-14 oxidation under SCR conditions. However, (NO)-N-14 was not detected when Fe-BEA was exposed to (NH3)-N-14 + O-2. Since the only source of N-14 derives from (NH3)-N-14, with the labeled gas mixture used, the (NO)-N-14 during SCR must have originated from oxidation of (NH3)-N-14. Furthermore, twice as much (NN)-N-14-N-14 was observed at 300 degrees C under SCR conditions in comparison with NH3 oxidation using O-2 alone. Under SCR conditions, the (NO)-N-14 formed through the unusual oxidation route further reacted with (NH3)-N-14 to produce N-14(2). Thus, for the first time, we have experimental evidence for the unusual overconsumption of ammonia during SCR over Fe-zeolites.
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| 24. |
- Nedyalkova, Radka, 1976, et al.
(författare)
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Improved low-temperature SCR activity for Fe-BEA catalysts by H2-pretreatment
- 2013
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 138, s. 373-380
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Tidskriftsartikel (refereegranskat)abstract
- A series of iron-exchanged zeolite beta catalysts (0.5 - 4 wt.-% Fe) have been prepared by incipient wetness impregnation and tested for selective catalytic reduction (SCR) of NOx with ammonia as reductant. The catalysts were characterized using BET, NH3-TPD and XPS before and after H2-pretreatment at 650°C for 5 h. The NH3-SCR activity tests show that the samples pretreated by hydrogen exhibit higher low-temperature SCR activity compared to the fresh samples, while the high-temperature activity remains almost constant. The results clearly show that the high-temperature H2-treatment has a significant influence on the extent of different iron species formed in the zeolite. Furthermore, H2-treatment of hydrothermally aged samples can recover some of the initial activity, although not completely due irreversible dealumination during the ageing. By H2-pretreatment SCR catalysts with high iron loading and high activity can be prepared.
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| 25. |
- Nedyalkova, Radka, 1976, et al.
(författare)
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Interzeolite Conversion of FAU Type Zeolite into CHA and its Application in NH3-SCR
- 2013
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 56:9-10, s. 550-557
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Tidskriftsartikel (refereegranskat)abstract
- In this work we studied the potential feasibility to synthesize small pore zeolites, such as chabazite (CHA) via interzeolite conversion of FAU type zeolite. We have thereafter used CHA as the starting material to obtain Cu-CHA. When CHA in NH4 (+) form was used to prepare Cu-CHA, the large size of the potassium cation present in the structure caused pore blockage in the chabazite framework, and diminished the adsorption and exchange capacity. However, Cu-CHA with comparable Selective Catalytic Reduction performance to the commercial catalyst was obtained via ion exchange if Cu-exchange was performed from H+-CHA form. Still, the main challenge was to fully eliminate K+ from the zeolite structure in order to further improve its catalytic performance and high temperature stability.
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| 26. |
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| 27. |
- Olsson, Louise, 1974, et al.
(författare)
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Kinetic modeling of sulfur poisoning and regeneration of lean NOx traps
- 2010
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 100:1-2, s. 31-41
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Tidskriftsartikel (refereegranskat)abstract
- Sulfur poisoning and regeneration of lean NOx traps were investigated using experiments and kinetic modeling. A commercial Pt, Rh and barium containing NOx storage catalyst was used. The catalyst also contained oxygen storage material. First the oxygen storage capacity (OSC) was investigated using steps with oxygen and hydrogen. The OSC was substantial with a total use of all hydrogen (1%) for about 20 s. The results were similar at the three investigated temperatures (300, 400 and 500 degrees C), indicating that it is a low activation barrier connected with the process. Further, no effect was observed when adding 15 ppm SO2 to the feed. Since no SO2 was observed in the outlet it is possible that SO2 is adsorbed during the lean period and then reduced to form H2S in the rich period (not measured). Further, the NOx storage was found to decrease during SO2 exposure, and the decrease was linear and dose dependent. In addition, we investigated different regeneration strategies. When using 500 ppm H-2 for 60 min at 700 degrees C the regeneration was poor. However, when adding 5% CO2 to the 500 ppm H-2 the regeneration was increased drastically. Further, the regeneration was decreased when decreasing the temperature to 600 degrees C, and further decreased when using 500 degrees C. In addition, it was beneficial with increasing the hydrogen concentration. The kinetic model contains three sub-models; (i)NOx storage and regeneration, (ii) oxygen storage and reduction and (iii) sulfur poisoning and sulfur regeneration. It was crucial to add NOx storage on two sites; barium and alumina. The NOx adsorbed on alumina is more loosely bound. Further, in the model formation of sulfates were added on both components. This was important in order to describe the rate of the sulfur deactivation. If sulfur was adsorbed only on barium the deactivation would have been too rapid. The model could describe the experimental features well.
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| 28. |
- Rasmuson, Anders, 1951, et al.
(författare)
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Mathematical Modeling in Chemical Engineering
- 2014
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- A solid introduction to mathematical modeling for a range of chemical engineering applications, covering model formulation, simplification and validation. It explains how to describe a physical/chemical reality in mathematical language and how to select the type and degree of sophistication for a model. Model reduction and approximation methods are presented, including dimensional analysis, time constant analysis and asymptotic methods. An overview of solution methods for typical classes of models is given. As final steps in model building, parameter estimation and model validation and assessment are discussed. The reader is given hands-on experience of formulating new models, reducing the models and validating the models. The authors assume the knowledge of basic chemical engineering, in particular transport phenomena, as well as basic mathematics, statistics and programming. The accompanying problems, tutorials, and projects include model formulation at different levels, analysis, parameter estimation and numerical solution.
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| 29. |
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| 30. |
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| 31. |
- Shwan, Soran, 1984, et al.
(författare)
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Chemical deactivation of Fe-BEA as NH3-SCR catalyst –Effect of Phosphorous
- 2014
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 147, s. 111-123
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Tidskriftsartikel (refereegranskat)abstract
- Fe-BEA as catalyst for selective catalytic reduction (SCR) of NOX with NH3 was experimentally studied with focus on chemical deactivation caused by phosphorous exposure.Cordierite supported Fe-BEA samples were exposed to 10 or 50 ppm H3PO4 for 14, 24 and 48 h in a continuous gas flow reactor at 350 C. The catalytic activity of the samples was studied by NH3- and NO-oxidation, NH3 inhibition and NH3-SCR experiments. The phosphorous exposed samples werefurther characterized by NH3- and NO-TPD, XPS and XRD. The results from the activity studies show that the degree of deactivation due to phosphorous exposure is strongly dependent on the exposure time, while the rate of deactivation is the same for exposure with 10 and 50 ppm H3PO4. The XPS results show that primarily phosphorous pentoxides (P2O5) are formed after short time of phosphorous exposure while longer time of exposure results in formation of metaphosphates (PO3-). The relativeamount of metaphosphates after 48 h of H3PO4 exposure was about 45 % compared to phosphorous pentoxides. The storage capacity of NO was shown to decrease with increasing relative amount of metaphosphates. The activity studies show that longer time of phosphorous exposure results in significantly decreased activity indicating that the active iron species are very sensitive to phosphorous forming metaphosphates. We suggest that metaphosphates replace the hydroxyl groups on the active iron species in Fe-BEA as the main mechanism for the decreased activity for NH3-SCR in connection with phosphorous exposure. Furthermore, the NH3 inhibition experiments show that the increased amount of strongly bound ammonia due to phosphorous exposure does not contribute to buffer the active iron sites with ammonia during transient SCR conditions.
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| 32. |
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| 33. |
- Shwan, Soran, 1984, et al.
(författare)
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Effect of post-synthesis hydrogen-treatment on the nature of iron species in Fe-BEA as NH3-SCR catalyst
- 2014
-
Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 4:9, s. 2932-2937
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Tidskriftsartikel (refereegranskat)abstract
- Post-synthesis treatment of Fe-BEA with hydrogen has previously been shown to improve the low-temperature activity for NO reduction during standard NH3-SCR. Here, a 2 wt.% Fe-BEA sample was prepared by incipient wetness impregnation and calcined in air at 450 °C for 3 h. The fresh sample was then treated with 5% H2 at 650 °C for 5 h. The evolution of different iron species in Fe-BEA before and after H2-treatment was studied using in situ DRIFT spectroscopy with NO as a probe molecule and by UV-Vis spectroscopy. The DRIFTS results show that the relative intensity of the absorption peak representing isolated iron species increases significantly after H2-treatment of the fresh Fe-BEA sample. Furthermore, the UV-Vis results show a significant decrease in the relative intensity in the UV region representing larger iron particles, whereas the relative intensity representing smaller iron species increases after treatment of Fe-BEA with hydrogen. The results show that the low-temperature NO reduction during standard NH3-SCR can be increased for Fe-BEA by redispersion of smaller iron species into the zeolite structure by hydrogen-treatment.
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| 34. |
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| 35. |
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| 36. |
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| 37. |
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| 38. |
- Shwan, Soran, 1984, et al.
(författare)
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Hydrothermal Stability of Fe−BEA as an NH3‑SCR Catalyst
- 2012
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 51:39, s. 12762−12772-12772
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Tidskriftsartikel (refereegranskat)abstract
- The hydrothermal stability of Fe−BEA as a selective catalytic reduction (SCR) catalyst was experimentallystudied. Cordierite supported Fe−BEA samples were hydrothermally treated at 600 and 700 °C for 3−100 h to capture the effect of aging time and temperature. Before and after aging the samples were characterized with BET, XPS, XRD, and NH3-TPD. The catalytic performance of the samples with respect to NO oxidation, NH3 oxidation, and NO reduction (NH3-SCR) was studied by flow reactor experiments to correlate changes of the catalytic performance with structural changes of the zeolite and the iron phases. The NH3-SCR experiments did not show any significant decrease in activity after a short time of aging (3 h at 700 °C)even though the ammonia storage capacity decreased by 40% and the oxidation state of iron slightly increased. A longer time of aging resulted in decreased activity for NO reduction during low temperatures (150−300 °C), while at higher temperatures(400−500 °C) the activity remained high. The results indicate that the NO reduction is more sensitive at low temperatures to changes in the oxidation state of iron caused by hydrothermal aging than at higher temperatures. Furthermore, a maximum in activity for NO oxidation and increased oxidation state of iron (Fe3+) indicate Fe2O3 particle growth.
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| 39. |
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| 40. |
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| 41. |
- Shwan, Soran, 1984, et al.
(författare)
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Influence of hydrothermal ageing on NH3-SCR over Fe-BEA -Inhibition of NH3-SCR by ammonia
- 2013
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 56:1-8, s. 80-88
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Tidskriftsartikel (refereegranskat)abstract
- The decay in ammonia adsorption capacity and the amount of active iron sites are important to consider in order to understand the deactivation processes of Fe-BEA as NH3-SCR catalyst. NH3 and NO storage capacity experiments together with kinetic modeling have been used to evaluate ammonia inhibition during NH3-SCR before and after hydrothermal treatment of H-BEA and Fe-BEA. The kinetic model shows that at least four types of acid sites for H-BEA and one additional site for Fe-BEA are required to predict the NH3 desorption well. NH3-TPD experiments together with simulations show that the strongest adsorption sites are the sites that are most affected by the hydrothermal treatment. For H-BEA a clear correlation between the ammonia storage capacity and the improved NOX conversion after NH3 cut-off during NH3-SCR is observed. However, Fe-BEA show an inhibiting effect of ammonia after NH3 cut-off but no significant difference (i.e. increased NOX conversion time) between fresh and aged samples can be observed, indicating that the inhibiting effect is unaffected by the hydrothermal treatment.
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| 42. |
- Shwan, Soran, 1984, et al.
(författare)
-
Inside front cover
- 2014
-
Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 4:9, s. 2688-2688
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Tidskriftsartikel (refereegranskat)
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| 43. |
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| 44. |
- Shwan, Soran, 1984, et al.
(författare)
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Kinetic modeling of H-BEA and Fe-BEA as NH3-SCR catalysts - Effect of hydrothermal treatment
- 2012
-
Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 197:1, s. 24-37
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Tidskriftsartikel (refereegranskat)abstract
- Kinetic modeling and flow reactor experiments were used to study the dynamic behavior of the active sites of H-BEA and Fe-BEA during NH3-SCR before and after hydrothermal aging of the catalysts. To capture transient changes it was crucial to describe NH3 and NO adsorption. For the H-BEA model the storage of ammonia was simplified to proceed on two zeolite sites representing weak and strong Brønsted acid sites, while NO only is adsorbed on Brønsted acid sites. Furthermore, the oxidation of NH3 and NO, and theNH3-SCR reaction are assumed to proceed over the Brønsted acid sites. To model Fe-BEA, monomeric and dimeric iron, and iron oxide particles represent sites of three different types of iron species. Ammonia and NO adsorb on monomeric iron which is assumed to be the governing site for low temperature SCR. Dimeric iron species provide the activity for high temperature SCR and NH3-oxidation. Furthermore, iron particles, Fe2O3, are not active for NH3-SCR but for oxidation of NO. A spillover mechanism of ammonia adsorbed on Brønsted acid sites to monomeric iron sites is included in the model to simulate the inhibiting effect of NH3 during the SCR reaction. The spillover rate was found to be independent of the site density and dependsonly on the fraction of free sites, indicating that a constant number of Brønsted acid sites buffer each activeiron site, unaffected by the hydrothermal treatment. The model describes the experiments well for HBEA and Fe-BEA before and after hydrothermal treatment by decreasing the site density and keeping the kinetic parameters constant except the binding energy of ammonia to Brønsted sites, which was found to decrease with hydrothermal treatment. Finally, the model was validated in separate ammonia inhibiting experiments, not used in the fitting process of the kinetic parameters. The aging model describes the validation experiments well.
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| 45. |
- Shwan, Soran, 1984, et al.
(författare)
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Kinetic Modeling of NOx Storage and Reduction Using Spatially Resolved MS Measurements
- 2014
-
Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 147, s. 1028-1041
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Tidskriftsartikel (refereegranskat)abstract
- A Global Kinetic NOX Storage and Reduction (NSR) Model based on flow reactor experiments was developed to investigate the NOX storage and reduction mechanisms with a focus on the breakthrough of NH3 and N2O during the rich phase. Intra-Catalyst Storage and Reduction Measurements (SpaciMS) were used to further validate the model, particularly with respect to the formation and utilization of ammonia along the catalyst axis. Two different catalysts were used in the model, denoted Cat. 1 and Cat. 2. The first catalyst was used in flow reactor experiments to create a global kinetic model and fitting the parameters using long NSR cycles validated against more realistic short NSR cycles, while the second catalyst was used in the SpaciMS experiments. However, due to some differences in the catalytic material, some parameters had to be re-tuned for the second catalyst. Two NOX storage sites were used for both catalysts, barium (Ba) and the support sites (S2). Furthermore, the Shrinking-Core Model was used to describe the mass transport of NOX inside the storage particles, S2. An oxygen storage component was necessarily included and denoted Ce for the first catalyst and representing ceria in the catalyst. The second catalyst did not contain any ceria, which is why the oxygen storage site was called S3 and can be interpreted as oxygen on the noble metal. During the rich period, NOX was reduced by H2 and CO, forming nitrogen and NH3. Produced NH3 reacted with stored NOX forming N2O and resulting in an N2O peak before NH3 breakthrough. The model agreed well with reactor experiments and SpaciMS measurements. The SpaciMS results showed that most NOX was stored in the first half of the catalyst, resulting in high ammonia production in the catalyst front and its subsequent consumption along the catalyst axis to reduce NOX stored downstream.
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| 46. |
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| 47. |
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| 48. |
- Sjövall, Hanna Maria, 1977, et al.
(författare)
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A Kinetic Model for the Selective Catalytic Reduction of NOx with NH3 over an Fe-zeolite Catalyst
- 2010
-
Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 49:1, s. 39-52
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Tidskriftsartikel (refereegranskat)abstract
- The selective catalytic reduction of NOx with ammonia over all Fe-zeolite catalyst was investigated experimentally and a transient kinetic model was developed. The model includes reactions that describe ammonia storage and oxidation, NO oxidation, selective catalytic reduction (SCR) of NO and NO2, formation of N2O, ammonia inhibition and ammonium nitrate formation. The model call account for a broad range of experimental conditions in the presence of H2O, CO2 and O-2 at temperatures from 150 to 650 degrees C. The catalyst stores ammonia at temperatures up to 400 degrees C and shows ammonia oxidation activity from 350 degrees C. The catalyst is also active for the oxidation of NO to NO2 and the oxidation reaches equilibrium at 500 degrees C. The SCR of NO is already active at 150 degrees C and the introduction of equal amounts of NO and NO2 greatly enhances the conversion of NOx at temperatures up to 300 degrees C. The formation of N2O is negligible if small fractions of NO2 are fed to the reactor, but a significant amount of N2O is formed at high NO2 to NO ratios. An ammonia inhibition oil the SCR of NO is observed at 200 degrees C. This kinetic model contains 12 reactions and is able to describe the experimental results Well. The model was validated using short transient experiments and experimental conditions not used in the parameter estimation and predicted these new conditions adequately.
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| 49. |
- Tamm, Stefanie, 1975, et al.
(författare)
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A kinetic model of the hydrogen assisted selective catalytic reduction of NO with ammonia over Ag/Al2O3
- 2013
-
Ingår i: AICHE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 59:11, s. 4325-4333
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Tidskriftsartikel (refereegranskat)abstract
- A global kinetic model which describes H2-assisted NH3-SCR over an Ag/Al2O3 monolith catalyst has been developed.The intention is that the model can be applied for dosing NH3 and H2 to an Ag/Al2O3 catalyst in a real automotiveapplication as well as contribute to an increased understanding of the reaction mechanism for NH3-SCR. Therefore, the model needs to be simple and accurately predict the conversion of NOx. The reduction of NO is described by a global reaction, with a molar stoichiometry between NO, NH3 and H2 of 1:1:2. Further reactions included in the model are the oxidation of NH3 to N2 and NO, oxidation of H2, and the adsorption and desorption of NH3. The model was fitted to the results of an NH3-TPD experiment, an NH3 oxidation experiment, and a series of H2-assisted NH3-SCR steady-state experiments. The model predicts the conversion of NOx well even during transient experiments.
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| 50. |
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