| 1. |
- Shishkin, Alexander, 1988, et al.
(författare)
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Functionalization of SSZ-13 and Fe-Beta with copper by NH3 and NO facilitated solid-state ion-exchange
- 2017
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Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 7:8, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- We show that functionalization of SSZ-13 (CHA) and Fe-beta (*BEA) with copper using a recently reported solid-state ion-exchange method, facilitated by NH3 and nitrogen oxides (NO), is a viable route to prepare Cu-SSZ-13 and (Cu + Fe)-beta catalysts, starting from H-SSZ-13 and Fe-beta, respectively. The physicochemical properties of the prepared catalysts are characterized by XRD, UV-Vis-spectroscopy and STEM-EDS, confirming that copper originally present in the physical mixture of CuO and H-SSZ-13, and CuO and Fe-beta, is inserted into the micropores of SSZ-13 and Fe-beta, respectively. Activity measurements in gas-flow reactor show that the samples are active for NO reduction by NH3-SCR over a broad temperature range, i.e., 150–500 C. For the Cu-SSZ-13 catalysts, which have a copper loading range of 0.5–4 wt. %, the sample prepared from the physical mixture with a CuO/SSZ-13 ratio corresponding to 2 wt.% Cu is the most active catalyst for NH3-SCR under the present reaction conditions. Furthermore, the (Cu + Fe)-beta catalyst shows higher NH3-SCR activity over a broader temperature range and especially at low temperature as compared to the Fe-beta and Cu-beta counterparts. The results encourage further elaboration on sequential ion-exchange procedures for bimetallic functionalization of zeolites.
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| 2. |
- Englund, Johanna, 1988, et al.
(författare)
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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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Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 9:12
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Tidskriftsartikel (refereegranskat)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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| 3. |
- 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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| 4. |
- Shishkin, Alexander, 1988, et al.
(författare)
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Improved Low- and High-temperature NH3-SCR Activity over Cu-CHA Prepared by Solid-state Ion-exchange Facilitated by NH3 and NO
- 2015
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Ingår i: EuropaCat XII, Kazan, Russia, 30 August - 4 September 2015.
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Konferensbidrag (refereegranskat)abstract
- This presentation will focus on optimizing the copper oxide concentration used in the physical mixture Before treatment. Furthermore, we are showing that Cu-CHA prepared by [NO+NH3]-SSIE can possess relatively high activity both for low- and high-temperature NH3-SCR compared to Cu-CHA prepared by conventional aqueous-based ion-exchange, even by using lower copper content. The study shows that the 2.0% Cu-CHA sample prepared by the [NO+NH3]-SSIE method possesses the highest NH3-SCR activity among the studied catalysts.
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| 5. |
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| 6. |
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| 7. |
- 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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| 8. |
- Shwan, Soran, 1984, et al.
(författare)
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Chemical deactivation of H-BEA and Fe-BEA as NH3-SCR catalysts - Effect of potassium
- 2015
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 166-167, s. 277-286
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Tidskriftsartikel (refereegranskat)abstract
- H-BEA and Fe-BEA were experimentally studied for selective catalytic reduction of NOx using ammonia (NH3-SCR) with focus on the chemical deactivation caused by potassium exposure where cordierite supported H-BEA and Fe-BEA samples were exposed to 10 or 50 ppm KNO3 for 14, 24 and 48 h in a continuous gas flow reactor at 3500C. The samples where catalytically evaluated and characterized using a flow-reactor system and X-ray photoelectron spectroscopy.The results show that new NOX storage sites are formed on the expense of Brønsted acid sites for ammonia storage for all potassium exposed samples. The formation of new NOX storage sites results in increased NH3-SCR activity for the potassium exposed H-BEA samples. However, for the potassium exposed Fe-BEA samples the results show a significant decrease in SCR activity. Deconvolution of the Fe 2p3/2 XPS peak shows a clear increase in the relative amount of Fe3+for the potassium exposed Fe-BEA samples, indicating that isolated iron species active for NH3-SCR are exchanged with potassium forming smaller trivalent iron clusters inside the zeolite pores. Transient experiments during NH3-SCR show that the decrease in ammonia storage capacity due to potassium exposure results in a decreased period with improved NO reduction after NH3 cut-off.
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| 9. |
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| 10. |
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| 11. |
- Shwan, Soran, 1984, et al.
(författare)
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Deactivation mechanisms of iron-exchanged zeolites for NH3-SCR applications
- 2015
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 258, s. 432-440
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Tidskriftsartikel (refereegranskat)abstract
- Emissions of nitrogen oxides (NOX) from internal combustion engines are a major contributor to global air pollution, and with more stringent environmental legislations, the need for more efficient and durable NOX emission control systems increases. In the present paper, experimental results of hydrothermal deactivation and regeneration using hydrogen, and chemical deactivation due to phosphorous and potassium exposure of Fe-BEA as NH3-SCR catalyst are summarized. Based on the experimental results, a multi-site kinetic model is developed to predict deactivation of Fe-BEA. The kinetic model predicts deactivation well by decreasing the number of active sites in the model representing loss of active iron sites due to migration or chemical blockage of the sites. It is discussed that by performing a systematic study of different deactivation mechanisms, a deactivation expression for the active sites could be formulated.
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| 12. |
- 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
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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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| 13. |
- Shwan, Soran, 1984, et al.
(författare)
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Effect of thermal ageing on the nature of iron species in Fe-BEA
- 2013
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Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 143:1, s. 43-48
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of NH3 and NO over fresh and thermally treated Fe-BEA catalysts were studied using in situ DRIFT spectroscopy to follow the evolution of different iron species before and after thermal treatment. Fe-BEA samples were prepared and thermally treated in air at 700 °C for 12, 24 and 48 h, and at 800 and 900 °C for 48 h. Compared to the fresh sample, the NH3 adsorption experiments indicate dealumination of the zeolite and iron oxide particle growth for the aged samples. Furthermore, the NO adsorption experiments show distinct absorption peaks which are assigned to isolated iron species, iron clusters and larger iron oxide particles. The thermally treated samples show migration of isolated iron species from the zeolite pores forming iron oxide particles. Further ageing results in a continuous migration and formation of larger iron oxide particles located on the external surface of the zeolite.
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| 14. |
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| 15. |
- Shwan, Soran, 1984
(författare)
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Fundamental deactivation mechanisms of Fe-BEA as NH3-SCR catalyst - Experimental studies and kinetic modeling
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Due to globalization and an increasing transport sector the interest for more fuel efficient combustion engines operating under lean conditions has increased. The products formed during the burning process in internal combustion engines are major contributants to global air pollution, where carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOX) are the major toxic components regulated in many countries. One effective way to reduce nitrogen oxides in lean environments is selective catalytic reduction with ammonia (NH3-SCR). Metal-exchanged zeolites have in this connection proven to be very active and promising catalysts for NOX reduction. Several challenges arise when using these materials in exhaust aftertreatment systems for vehicles. One problem is thermal deactivation due to the high-temperature conditions in connection with the regeneration of the particulate filter which in addition to the SCR catalyst is an important component in the aftertreatment system. In this licentiate thesis, the thermal stability of iron-based zeolite beta, Fe-BEA, as NH3-SCR catalyst is evaluated with several different experimental techniques. Based on the experimental results a kinetic model is developed to describe the kinetics and the fundamental deactivation mechanisms for Fe-BEA after hydrothermal treatment with focus on the dynamics of the active iron sites. Cordierite supported Fe-BEA samples were hydrothermally treated at 600 and 7000C for 3-100 h to capture the effect of time and temperature on the ageing process. The samples were characterized with BET, XPS, XRD and NH3-TPD. The catalytic performance of the samples with respect to NO and NH3 oxidation, and NOX reduction (NH3-SCR) was studied by flow reactor experiments. The catalytic performance was correlated with structural changes of the zeolite and the iron phases. The results showed that the NOX reduction at low temperatures is more sensitive to changes in the oxidation state of iron caused by the hydrothermal ageing than at higher temperatures. Furthermore, a maximum in activity for NO oxidation and an increased oxidation state of iron indicate Fe2O3 particle growth. This was further investigated with DRIFT spectroscopy which showed that the change of the nature of the iron species in Fe-BEA proceeds in two steps; (i) milder ageing results in a decreased amount of isolated iron species due to migration, and (ii) more sever aging results in a continuous migration and formation of larger iron oxide particles. High surface coverage of ammonia inhibits the SCR reaction. However, the inhibition effect is not significantly affected by the hydrothermal treatment. Furthermore, the possibility to regenerate the catalyst by treatment with hydrogen was investigated. The H2-treatment showed a reversed trend compared to the hydrothermally treated samples. Increased NOX reduction at low temperatures was observed indicating that the H2-treatment results in the formation of isolated iron species in the zeolite.A kinetic ageing model was developed based on the experimental results for H-BEA and Fe-BEA. The ageing model describes the experiments well for both H-BEA and Fe-BEA, before and after hydrothermal treatment, by decreasing the density of active sites. Furthermore, the model showed that the spillover rate of ammonia, inhibiting the NOX reduction is independent of the site density and depends only on the fraction of free sites, indicating that a constant number of Brønsted sites buffer each active iron site is constant and unaffected by the hydrothermal treatment.
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| 16. |
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| 17. |
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| 18. |
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| 19. |
- 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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| 20. |
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| 21. |
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| 22. |
- Shwan, Soran, 1984, et al.
(författare)
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Impact of Thermal and Chemical Ageing of Fe-BEA SCR Catalyst on NOx Conversion Performance
- 2016
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Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 9:2, s. 1305-1313
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Tidskriftsartikel (refereegranskat)abstract
- Emissions of nitrogen oxides (NOx) from heavy-duty diesel engines are subject to more stringent environmental legislation. Selectivecatalytic reduction (SCR) over metal ion-exchanged zeolites is in this connection an efficient method to reduce NOx. Understandingdurability of the SCR catalyst is crucial for correct design of the aftertreatment system. In the present paper, thermal and chemicalageing of Fe-BEA as NH3-SCR catalyst is studied. Experimental results of hydrothermal ageing, and chemical ageing due tophosphorous and potassium exposure are presented. The catalyst is characterized by flow reactor experiments, nitrogen physisorption,DRIFTS, XRD, and XPS. Based on the experimental results, a multisite kinetic model is developed to describe the activity of the freshFe-BEA catalyst. Furthermore, the model can predict deactivation of the catalyst well by decreasing the number of active sites,representing loss of active iron sites due to migration or chemical blockage of the sites. By performing a systematic study of differentdeactivation mechanisms, a deactivation expression for the active sites can be formulated.
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| 23. |
- 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
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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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| 24. |
- Shwan, Soran, 1984, et al.
(författare)
-
Inside front cover
- 2014
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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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| 25. |
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| 26. |
- Shwan, Soran, 1984, et al.
(författare)
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Kinetic modeling of Fe-BEA as NH3-SCR catalyst – Effect of Phosphorous
- 2015
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Ingår i: AICHE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 61:1, s. 215-223
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Tidskriftsartikel (refereegranskat)abstract
- The focus of this work is to investigate whether a previously developed micro-kinetic deactivation model for hydrothermally treated Fe-BEA as NH3-SCR catalyst can be applied to describe chemical deactivation of Fe-BEA due to phosphorous exposure. The model describes the experiments well for Fe-BEA before and after phosphorous exposure by decreasing the site density, representing deactivation of sites due to formation of metaphosphates blocking the active iron sites, while the kinetic parameters are kept constant. Furthermore, the results show that the activity for low-temperature SCR is very sensitive to loss of active monomeric iron species due to phosphorous poisoning compared to high-temperature SCR. Finally, the ammonia inhibition simulations show that exposure to phosphorous may affect the internal transport of ammonia between ammonia storage sites buffering the active iron sites which results in a lower SCR performance during transient conditions.
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| 27. |
- 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
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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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| 28. |
- Shwan, Soran, 1984, et al.
(författare)
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Kinetic Modeling of NOx Storage and Reduction Using Spatially Resolved MS Measurements
- 2014
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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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| 29. |
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| 30. |
- Shwan, Soran, 1984
(författare)
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Metal-exchanged zeolites for NH3-SCR applications - Activity and Deactivation studies
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Emissions of nitrogen oxides (NOX) formed during the burning process in internal combustion engines is a major contributor to global air pollutions. One effective way to reduce NOX in lean environments, i.e. oxygen excess is selective catalytic reduction with ammonia (NH3-SCR). Metal-exchanged zeolites have proven to be active as SCR catalysts, where copper and iron are the most common metals. When using metal-exchanged zeolites in exhaust aftertreatment systems, several challenges arise. Resistance towards hydrothermal deactivation and chemisorption of impurities on the active sites of the catalyst are two of the more important challenges. Temperatures between 600-700oC can be seen during regeneration of the particulate filter, which usually is placed upstream close to the SCR catalyst in the exhaust aftertreatment system, and therefore hydrothermal stability of the metal-exchanged zeolite is crucial. Furthermore, high tolerance against catalyst poisons which originate from (bio-) fuels and lubricating oils is desired, where phosphorous and potassium are among the more important poisons. In this thesis thermal and chemical deactivation of iron-exchanged zeolite BEA as SCR catalyst is experimentally studied with special focus paid on the active iron species. Based on the experimental results a kinetic model is developed to predict the decreased activity of the catalyst after deactivation. Several characterization techniques are used to evaluate and correlate structural changes in the catalyst with the decreased activity. Catalysts are prepared and characterized using BET, XPS, XRD, TPD, in-situ FTIR and UV-Vis. The catalytic performance of the samples is measured using a flow-reactor system.It is concluded that the hydrothermal deactivation of Fe-BEA is a result of migration of isolated iron species forming iron cluster inside the zeolite pores and iron particles located on the external surface of the zeolite crystals. Further, it is shown that the growth of iron clusters and particles can be partially reversed by high temperature hydrogen treatment. The chemical deactivation due to phosphorous exposure is the result of formation of metaphosphates replacing hydroxyl groups on the active isolated iron species. Furthermore, the chemical deactivation of Fe-BEA by potassium is concluded to be due to exchange and loss of active isolated iron species in the zeolite forming smaller iron clusters inside the zeolite pores.A kinetic model where different iron species are included was developed based on the hydrothermal deactivation experiments and validated using phosphorous and potassium exposed samples. By fitting and fix the kinetic parameters towards a fresh sample, the decreased SCR activity can be predicted by just decreasing the number of active iron sites, representing loss of active iron species due to hydrothermal treatment and poisoning.The effect of gas atmosphere during solid-state ion-exchange of copper-zeolites was studied as well. It is concluded that copper becomes highly mobile due to formation of copper-ammine complexes in presence of NH3 after reduction of CuII to CuI by adding NO in the exposing gas during the solid-state ion-exchange. Copper-exchanged zeolites could be prepared by exposing physical mixtures of copper-oxides with zeolites to NO and NH3 at as low temperature as 250oC.Finally, the ammonia formation during the rich period of NOX storage and reduction (NSR) cycles was studied using kinetic modeling for the possibility of combining NSR and SCR catalysts in the exhaust aftertreatment system. It is concluded that the formation of ammonia is due to stored NOX and hydrogen from the gas in the first half of the catalyst. However, it was further concluded that the formation of ammonia is delayed due to formation of N2O from stored NOX and formed NH3.
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| 31. |
- Shwan, Soran, 1984, et al.
(författare)
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NH3-SCR activity of H-BEA and Fe-BEA after potassium exposure
- 2015
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 58:14-17, s. 1012-1018
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Tidskriftsartikel (refereegranskat)abstract
- A previous developed multisite microkinetic model for hydrothermally deactivated H-BEA and Fe-BEA catalyst used for NH3-SCR applications has been applied and validated using potassium exposed H-BEA and Fe-BEA samples. The catalysts have been exposed to evaporated aqueous solution of potassium (10 ppm KNO3) in a flow-reactor for 14-48 h. The results for the H-BEA samples show an increase in NH3-SCR activity after 48 h of potassium exposure. This is correlated to an increase in NOX storage capacity, indicating that potassium forms new NOX storage sites participating in the SCR reaction. However, the Fe-BEA samples show different results. The SCR activity for the Fe-BEA catalyst decreases significantly after 14 h of exposure to potassium and after longer exposure time the activity slightly increases again compared to the sample exposed to potassium for 14 h. When applying the kinetic model to the flow-reactor measurements the model is able to predict the changes in SCR activity well when changing the site density of the active sites. In overall, combining the experimental results with the simulation indicates that exposure to potassium initially chemically blocks the active iron species which decrease with exposure time. Longer time of exposure to potassium indicates that the iron species are exchanged and lost due to formation of new potassium sites in the zeolite resulting in an overall lower SCR activity compared to a fresh Fe-BEA sample.
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| 32. |
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| 33. |
- Shwan, Soran, 1984, et al.
(författare)
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Solid-State Ion-Exchange of Copper into Zeolites Facilitated by Ammonia at Low Temperature
- 2015
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 5:1, s. 16-19
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the gas phase during solid-state ion-exchange of copper into zeolites was studied by exposing physical mixtures of copper oxides (CuI2O and CuIIO) and zeolites (MFI, *BEA and CHA) to various combinations of NO, NH3, O2 and H2O. It is shown that heating these mixtures to 250°C results in active catalysts for the selective catalytic reduction of NO with NH3 (NH3-SCR), indicating that the Cu has become mobile at that temperature. Such treatment allows for a fast (
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- Skoglundh, Magnus, 1965, et al.
(författare)
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Copper mobility in zeolite-based SCR catalysts
- 2017
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Ingår i: Presented at the 254th American Chemical Society National Meeting & Exposition, Washington D.C., USA, August 20-24, 2017.
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Konferensbidrag (refereegranskat)abstract
- Selective catalytic reduction with ammonia (NH3-SCR) is an effective, well-established method to eliminate nitrogen oxides (NOx) in oxygen excess for stationary and mobile applications. Titania-supported vanadia catalysts are traditionally used for NH3-SCR. This type of catalyst is effective in the range 300-450°C, but the NOx reduction efficiency decreases at both lower and higher temperatures. The efficiency of the NH3-SCR process can be improved significantly by using catalysts based on copper-exchanged zeolites and zeotypes, due to their high activity around 200°C. Solid-state ion-exchange in a mixture of copper oxide and zeolite is an efficient way to prepare such catalysts, but this process usually requires high (>700°C) temperatures. The ion-exchange can be considerably affected by appropriate choice of atmosphere during the process. It is shown that the copper-exchange is possible at unprecedented low temperatures, as low as 250°C, in presence of ammonia. The influence of the treatment conditions on the copper-exchange and the mechanism of the reaction-driven ion-exchange process will be presented and discussed. Such copper-exchanged zeolite structures with high copper loading are potentially interesting catalysts for a number of technical applications.Powder mixtures of Cu2O or CuO and zeolite with either CHA, MFI or *BEA framework structure were exposed to well-defined gas atmospheres at constant temperature. After the treatment, the SCR activity of the samples was determined by steady state and transient flow reactor experiments, and the physicochemical properties of the samples were characterized with bulk and surface sensitive characterization techniques. Furthermore, first-principles calculations were used to investigate the energetic conditions for the ion-exchange process.We show that in the presence of ammonia, copper becomes mobile at considerably lower temperatures,
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| 36. |
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| 37. |
- Skoglundh, Magnus, 1965, et al.
(författare)
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Mobility of copper in zeolite-based SCR catalysts
- 2017
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Ingår i: Presented at the 25th North American Catalysis Society Meeting, Denver, Colorado, USA, June 4-9 2017.
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Konferensbidrag (refereegranskat)abstract
- Selective catalytic reduction with ammonia (NH3-SCR) is a well-established and effective method to eliminate nitrogen oxides (NOx) in oxygen excess for stationary and mobile applications. Vanadia supported on titania was the first NH3-SCR catalyst that was commercialized. This type of catalyst is effective around 300-450°C, however at lower or higher temperatures, the efficiency of the catalyst to reduce NOx decreases. To increase the overall NOx reduction, high SCR activity around 200°C is required and copper-exchanged zeolites are interesting candidates in this respect. Solid-state ion-exchange in a mixture of copper oxide and zeolite is an efficient method to prepare such catalysts, but the process usually requires high (>700°C) temperatures. The ion-exchange process with copper oxides and zeolites can be considerably affected inpresence of reactive atmospheres. It is shown that the copper-exchange is possible at unprecedented low temperatures, as low as 250°C, when facilitated by ammonia. The influence of the treatment conditions on the copper-exchange and the mechanism of the ion-exchange process will be presented and discussed. Such copper-exchanged zeolite structures with high copper loading are potentially interesting catalysts for a number of technical applications.Powder mixtures of CuO or Cu2O and zeolite with either the MFI, *BEA or CHA framework structure were exposed to well-defined gas atmospheres at constant temperature. After the treatment the SCR activity was determined by steady state and transient flow reactor experiments, and the physico-chemical properties of the samples were characterized with bulk and surface sensitive characterization techniques. Furthermore, density functional theory calculations were used to investigate the energetic conditions for the ion-exchange process. We show that copper in the presence of ammonia becomes mobile at considerably lower temperatures,
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