| 1. |
- Feizie Ilmasani, Rojin, 1989, et al.
(författare)
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Investigation of CO Deactivation of Passive NOx Adsorption on La Promoted Pd/BEA
- 2022
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Ingår i: Emission Control Science and Technology. - : Springer Science and Business Media LLC. - 2199-3629 .- 2199-3637. ; 8:1-2, s. 63-77
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Tidskriftsartikel (refereegranskat)abstract
- Passive NOx adsorption (PNA) is a method, in which NOx can be stored at low temperatures and released at higher temperatures where the urea decomposition is functional during selective catalytic reduction (i.e., above 180–200 °C). We have studied the promotion of Pd/BEA with La as a PNA in the presence of high CO concentration. Both the reference and promoted samples exhibited a significant loss of NOx adsorption/desorption capacity after multiple cycles using 4000 ppm CO. However, already after 5 cycles, 99% of the NOx released between 200 and 400 °C was lost for Pd/BEA, compared to only 64% for Pd-La/BEA, which thereafter was stable. XPS and O2-TPD clearly showed that the Pd species were influenced by La. The PNA deactivation in the presence of CO could be related to Pd reduction followed by migration and the formation of more PdOx clusters, as observed by O2-TPD analysis. Interestingly, significantly more PdOx clusters formed on Pd/BEA after 10 cycles compared to Pd-La/BEA.
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| 2. |
- Jonsson, Rasmus, 1989, et al.
(författare)
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The Impact of Lanthanum and Zeolite Structure on Hydrocarbon Storage
- 2021
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Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 11:5
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Tidskriftsartikel (refereegranskat)abstract
- Hydrocarbon traps can be used to bridge the temperature gap from the cold start of a vehicle until the exhaust after-treatment catalyst has reached its operating temperature. In this work, we investigate the effect of zeolite structure (ZSM-5, BEA, SSZ-13) and the effect of La addition to H-BEA and H-ZSM-5 on the hydrocarbon storage capacity by temperature-programmed desorption and DRIFT spectroscopy. The results show that the presence of La has a significant effect on the adsorption characteristics of toluene on the BEA-supported La materials. A low loading of La onto zeolite BEA (2% La-BEA) improves not only the toluene adsorption capacity but also the retention of toluene. However, a higher loading of La results in a decrease in the adsorbed amount of toluene, which likely is due to partial blocking of the pore of the support. High loadings of La in BEA result in a contraction of the unit cell of the zeolite as evidenced by XRD. A synergetic effect of having simultaneously different types of hydrocarbons (toluene, propene, and propane) in the feed is found for samples containing ZSM-5, where the desorption temperature of propane increases, and the quantity that desorbed increases by a factor of four. This is found to be due to the interaction between toluene and propane inside the structure of the zeolite.
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| 3. |
- Wang, Aiyong, 1989, et al.
(författare)
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A deactivation mechanism study of phosphorus-poisoned diesel oxidation catalysts: Model and supplier catalysts
- 2020
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 10:16, s. 5602-5617
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Tidskriftsartikel (refereegranskat)abstract
- The effect of phosphorus poisoning on the catalytic behavior of diesel oxidation catalysts was investigated over model and supplier monolith catalysts, i.e., Pd-Pt/Al2O3. The results of ICP and XPS from the vapor-phase poisoning over model catalysts suggested that the temperature of phosphorus poisoning affects both the overall content of phosphorus and the dispersion of phosphorus (i.e., inlet/outlet and surface/bulk). Phosphorus oxide (P2O5), metaphosphate (PO3-), and phosphate (PO43-) were identified in the poisoned model and supplier catalysts. The distribution of these species on poisoned model catalysts was highly dependent on the poisoning temperature, i.e., a higher temperature resulted in a higher concentration of PO43-. The outlets of the monoliths contained more PO43- and less P2O5 than the inlets. Both active sites and surface OH groups on model and supplier catalysts were contaminated upon phosphorus poisoning. It is found that PO43- had a stronger influence on the active sites than P2O5. One significant finding in this study is that the vapor-phase phosphorus poisoning could be a practical and cost efficient approach to simulate an accelerated aging/poisoning process.
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| 4. |
- Wang, Aiyong, 1989, et al.
(författare)
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Insight into hydrothermal aging effect on Pd sites over Pd/LTA and Pd/SSZ-13 as PNA and CO oxidation monolith catalysts
- 2020
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 278
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Tidskriftsartikel (refereegranskat)abstract
- In this study, Pd/LTA and Pd/SSZ-13 were prepared and then hydrothermally aged at the temperature of 750, 800, 850, and 900 °C. Multiple Pd species, including isolated Pd ions (Pd2+ and [Pd(OH)]+) and 1∼2 nm PdOx nanoparticles, were presented in two fresh samples. The Pd/LTA sample showed remarkable hydrothermal stability, but the Pd/SSZ-13 sample experienced severe damage after aging at 900 °C. The destruction of the aged Pd/SSZ-13 sample led to the migration and sintering of PdOx nanoparticles, which formed bulk PdOx particles on the surface of the zeolite crystallite. A large number of PdOx nanoparticles were retained after aging of the Pd/LTA sample. Pd/LTA contained a higher concentration of Pd2+ sites, while Pd/SSZ-13 had more [Pd(OH)]+ sites. It is found that the improvement of NO adsorption ability with CO addition onto Pd2+ was more significant than onto [Pd(OH)]+.
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| 5. |
- Yao, Dawei, 1991, et al.
(författare)
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Kinetic modeling of CO assisted passive NOx adsorption on Pd/SSZ-13
- 2022
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 428
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Tidskriftsartikel (refereegranskat)abstract
- Passive NOx adsorption (PNA) has been recently developed as a promising technology for controlling the NOx emissions during the cold start period. In this work, we illustrate a CO-assisted mechanism by combining experimental and kinetic modeling studies. Pd/SSZ-13 has been synthesized, characterized and evaluated as a PNA in low-temperature NOx adsorption and temperature program desorption cycles, to represent multiple cold start periods. The gas compositions were also systemically changed, where both the effect of varying NOx and CO feed was evaluated in the presence of high water and oxygen contents. A kinetic model was developed to simulate the profiles of NO and NO2, including three initial Pd sites (Z-Pd(II)Z-, Z-[Pd(II)OH]+ and PdO). It is concluded from XPS and in situ DRIFTS experiments, flow reactor measurements and modelling observations that CO reduces Pd(II) species to Pd(I)/Pd(0) species, which increases the stability of the stored NOx species, resulting in a release above the urea dosing temperature. The model could well describe the experimental features, including the effect of CO. In addition, the model was used for full-scale catalytic converter simulations.
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| 6. |
- Friberg, Ida, 1990, et al.
(författare)
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Hydrothermal Aging of Pd/LTA Monolithic Catalyst for Complete CH4 Oxidation
- 2020
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Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 10:5
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Tidskriftsartikel (refereegranskat)abstract
- Palladium-based catalysts are known to provide high CH4 oxidation activity. One drawback for these materials is that they often lose activity in the presence of water vapor due to the formation of surface hydroxyls. It is however possible to improve the water vapor tolerance by using zeolites as support material. In this study, we have investigated Pd supported on thermally stable LTA zeolite with high framework Si/Al ratio (Si/Al = ~44) for CH4 oxidation and the effect of hydrothermal aging at temperatures up to 900◦C. High and stable CH4 oxidation activity in the presence of water vapor was observed for Pd/LTA after hydrothermal aging at temperatures ≤ 700◦C. However, aging at temperatures of 800–900◦C resulted in catalyst deactivation. This deactivation was not a result of structural collapse of the LTA zeolite as the LTA zeolite only showed minor changes in surface area, pore volume, and X-ray diffraction pattern after 900◦C aging. We suggest that the deactivation was caused by extensive formation of ion-exchanged Pd2+ together with Pd sintering. These two types of Pd species appear to have lower CH4 oxidation activity and to be more sensitive to water deactivation compared to the well dispersed Pd particles observed on the LTA support prior to the hydrothermal aging. By contrast, Pd/Al2O3 was generally sensitive to water vapor no matter of the aging temperature. Although the aging caused extensive Pd sintering in Pd/Al2O3, only minor deterioration of the CH4 oxidation activity was seen. The results herein presented show that Pd/LTA is a promising CH4 oxidation catalyst, however Pd rearrangement at high temperatures (≥800◦C) is one remaining challenge.
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| 7. |
- Han, Joonsoo, 1990, et al.
(författare)
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N 2 O Formation during NH 3 -SCR over Different Zeolite Frameworks: Effect of Framework Structure, Copper Species, and Water
- 2021
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 60:49, s. 17826-17839
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Tidskriftsartikel (refereegranskat)abstract
- The formation characteristics of N2O were investigated with respect to copper-functionalized zeolites, i.e., Cu/SSZ-13 (CHA), Cu/ZSM-5 (MFI), and Cu/BEA (BEA) and compared with the corresponding zeolites in the H form as references to elucidate the effect of the framework structure, copper addition, and water. Temperature-programmed reduction with hydrogen showed that the CHA framework has a higher concentration of Cu2+ (Z2Cu) compared to MFI and BEA. The characterizations and catalyst activity results highlight that CHA has a framework structure that favors high formation of ammonium nitrate (AN) in comparison with MFI and BEA. Moreover, AN formation and decomposition were found to be promoted in the presence of Cu species. On the contrary, lower N2O formation was observed from Cu/CHA during standard and fast SCR reactions, which is proposed to be due to highly stabilized AN inside the zeolite cages. On the other hand, significant amounts of N2O were released during heating due to decomposition of AN, implying pros and cons of AN stability for Cu/CHA with possible uncontrolled N2O formation during transient conditions. Additionally, important effects of water were found, where water hinders AN formation and increases the selectivity for decomposition to NO2 instead of N2O. Thus, less available AN forming N2O was observed in the presence of water. This was also observed in fast SCR conditions where all Cu/zeolites exhibited lower continuous N2O formation in the presence of water.
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| 8. |
- Isapour Toutizad, Ghodsieh, 1986, et al.
(författare)
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In situ DRIFT studies on N2O formation over Cu-functionalized zeolites during ammonia-SCR
- 2022
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 12:12, s. 3921-3936
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the zeolite framework structure on the formation of N2O during ammonia-SCR of NOx was studied for three different copper-functionalized zeolite samples, namely Cu-SSZ-13 (CHA), Cu-ZSM-5 (MFI), and Cu-BEA (BEA). The evolution of surface species during the SCR reaction at different temperatures was monitored with step-response experiments using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) at different reaction conditions. Also, density functional theory (DFT) calculations were performed to assist the interpretation of the experimental results. The DRIFTS results indicate that NO+ and nitrate species are the main products formed during NO oxidation, and NO appears to adsorb on both Cu-Lewis and Al-Lewis acid sites. The DFT calculations for NO adsorption on the SSZ-13 sample reveal adsorption at Bronsted acid sites with similar adsorption energies but with a slight difference in NO+ stretching vibrations in the DRIFT spectra. Within the standard SCR reaction, in the O-H stretching region, the number of NH3 molecules adsorbed on the Bronsted acid sites is higher for the small-pore size sample compared to the medium- and large-pore zeolites. The obtained DRIFTS results for nitrate species are supported by DFT calculations by simulating the IR spectra of mobile and framework bound nitrate species, which both have a signature at 1604 cm(-1) associated with the O-N bond on NO3-. It is revealed that N2O is produced in a higher amount at lower temperatures for all three samples irrespective of the NO/NO2 ratio. Furthermore, the obtained results from both DRIFTS studies and flow reactor experiments show the higher formation of N2O for the large-pore zeolite compared to the medium- and small-pore zeolite.
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| 9. |
- Wang, Aiyong, 1989, et al.
(författare)
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Deactivation mechanism of Cu active sites in Cu/SSZ-13 — Phosphorus poisoning and the effect of hydrothermal aging
- 2020
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 269
-
Tidskriftsartikel (refereegranskat)abstract
- Non-poisoned and P-poisoned Cu/SSZ-13 catalysts with different types of Cu sites, i.e., [Cu(OH)]+ and Cu2+, were investigated for NH3-SCR. Phosphorus was found to interact more with [Cu(OH)]+ than Cu2+. Moreover, less phosphorus was required per Cu for poisoning in the samples with a high content of [Cu(OH)]+. We propose a phosphorus poisoning mechanism based on H2-TPR and XPS: poisoning of one Cu2+ involved two P atoms, i.e., P2O5, but for [Cu(OH)]+ contamination, only one P atom (PO3− or PO43−) is needed. Furthermore, phosphorus poisoning resulted in a decline in NH3/NO oxidation and an improvement in SCR activity at high temperatures. Upon hydrothermal aging, [Cu(OH)]+−phosphate/metaphosphate complexes were likely easier detached from the framework than the Cu2+−P2O5 species. This resulted in that the P-poisoned catalyst with high content [Cu(OH)]+ experienced more severe deactivation and dealumination than the non-poisoned catalyst. Additionally, 27Al-NMR suggested that the formation of AlPO4 has a linear relationship with [Cu(OH)]+/Cu2+ ratios.
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| 10. |
- Wang, Aiyong, 1989, et al.
(författare)
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Insight into the effect of phosphorus poisoning of Cu/zeolites with different framework towards NH 3 -SCR
- 2023
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 454
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Tidskriftsartikel (refereegranskat)abstract
- Cu/zeolites were prepared to elucidate the effect of phosphorus poisoning on different zeolite framework structures for NH3-SCR. The results show that there are significant differences in phosphorus poisoning depending on the zeolite framework structure. The PO3−/PO43− species gradually decreased along with an increase in P2O5 in the following order: Cu/SSZ-13, Cu/ZSM-5, and Cu/BEA. One possible reason could be the increased pore size of these zeolites, which results in less steric hindrance for larger P2O5 species. P2O5 is suggested to enhance the redox ability of Cu ions, which results in an increase in low-temperature activity in NH3-SCR, whereas Cu ions were significantly poisoned by PO3−/PO43−, resulting in low-temperature deactivation. Furthermore, the effect of phosphorus poisoning on the structure of Cu/ZSM-5 was found to be much greater than that of Cu/BEA and Cu/SSZ-13, possibly due to phosphorus attacked the surface defects of the zeolite, causing local expansion and cracking.
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| 11. |
- Wang, Aiyong, 1989, et al.
(författare)
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Insight into the SO2 poisoning mechanism for NOx removal by NH3-SCR over Cu/LTA and Cu/SSZ-13
- 2020
-
Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 395
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Tidskriftsartikel (refereegranskat)abstract
- In this study, Cu/LTA and Cu/SSZ-13 catalysts are examined for sulfur poisoning and regeneration. The nature of the Cu species was probed with H2-TPR and in-situ DRIFTS. These characterizations collectively indicate that primarily Z2Cu is present in Cu/LTA, whereas Cu/SSZ-13 contains a higher concentration of ZCuOH. ZCuOH is proved to be more vulnerable to SO2 poisoning than Z2Cu sites in both Cu/zeolites. H2-TPR results suggest that the interaction of ZCuOH with the framework in Cu/LTA is much weaker than in Cu/SSZ-13, thereby leading to more susceptibility to SO2adsorption. Moreover, Cu/LTA can store more SO2 under NH3-SCR conditions in the presence of SO2, and it also has a slower deactivation rate due to the different location of generated (NH4)2SO4. Cu/LTA can be fully restored after regeneration at 750°C. However, Cu/SSZ-13 experiences a loss of activity at high temperature, which is attributed to newly formed CuOx clusters.
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| 12. |
- Wang, Aiyong, 1989, et al.
(författare)
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Investigation of the robust hydrothermal stability of Cu/LTA for NH3-SCR reaction
- 2019
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 246, s. 242-253
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Tidskriftsartikel (refereegranskat)abstract
- Recently copper ion-exchanged LTA zeolites were proved to be robust for NH3-SCR reaction. In this study, Cu/LTA catalysts with Si/Al = 15 and Cu/Al = 0.4 were synthesized via incipient wetness impregnation (IWI) method, following degreening/hydrothermal aging at different temperatures (750, 800, 850, 900 °C), and used to catalyze standard SCR, fast SCR and NH3/NO oxidation reactions. Catalysts were characterized with surface area/pore volume, powder X-Ray diffraction (XRD), nuclear magnetic resonance (NMR), H2-temperature programmed reduction (H2-TPR) and in situ Diffuse Reflectance Infrared Fourier Transform Spectra (DRIFTS). Through the BET surface areas, XRD and NMR results, it can be found that the framework structure stability of Cu/LTA catalysts during hydrothermal aging was outstanding, even after harsh aging at 900 °C. Moreover, various Cu species, including Z-Cu2+, Z-[Cu(OH)]+ and CuOx clusters, were quantified for Cu/LTA catalysts hydrothermally aged under various temperatures with H2-TPR and in situ DRIFTS. An imperative finding in this study is the exceptional hydrothermal stability of [Cu(OH)]+ and the gradual conversions of both Cu2+ and CuOx clusters to [Cu(OH)]+ with increasing aging temperature. It is worth noting that this phenomenon is exactly the opposite of Cu/SSZ-13. As it is known from the literature (Song et al., 2017), the formation of CuOx not only decreases the selectivity of NOx conversion, but also can cause deterioration of zeolite structure, since the ion-exchanged copper stabilizes the zeolite. This may also explain why the hydrothermal stability of Cu/LTA samples is outstanding.
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| 13. |
- Wang, Aiyong, 1989, et al.
(författare)
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Layered Pd/SSZ-13 with Cu/SSZ-13 as PNA − SCR dual-layer monolith catalyst for NOx abatement
- 2021
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 360, s. 356-366
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Tidskriftsartikel (refereegranskat)abstract
- A concept of a layered Pd/SSZ-13 with Cu/SSZ-13 as PNA-SCR dual-layer monolith catalyst for NOx abatement is demonstrated. NO-TPD was employed for determining the NOx storage, and the samples are characterized in detail using SEM-EDX, CO/NO-DRIFTS, XPS and H2-TPR. 750 °C hydrothermal treatment greatly promotes the NOx storage capacity and the addition of CO promotes NOx storage capacity and also shifts the NOx desorption temperature. The dual-layer sample (Pd/SSZ-13+Cu/SSZ-13) maintains most of the NOx storage capacity while the NOx desorption temperature is modified due to Cu/SSZ-13 as the top layer. The layered sample work well for NH3-SCR reaction. Notably, for Pd/SSZ-13+Cu/SSZ-13, more than 80 % of the NOx trapped at low temperature (i.e., 80 °C) can desorb in the suitable SCR temperature region where NOx conversion higher than 80 % is found. However, some loss of NO storage is found after SCR experiments. Overall, the dual-layer concept shows interesting potential for NOx abatement, but requires further developments on the PNA material to ensure stable storage capacity.
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| 14. |
- Wang, Aiyong, 1989, et al.
(författare)
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The impact of automotive catalysis on the United Nations sustainable development goals
- 2019
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Ingår i: Nature Catalysis. - : Springer Science and Business Media LLC. - 2520-1158. ; 2:7, s. 566-570
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Catalysis is essential in the automotive and transportation sectors to target the United Nations sustainable development goals for climate change and the environment. To comply with both the ambitious United Nations goals and step-by-step stringent emission regulations, innovative and economically viable catalytic systems will be a key element in meeting these challenges.
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| 15. |
- Woo, Jung Won, 1980, et al.
(författare)
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Impact of Different Synthesis Methods on the Low-Temperature Deactivation of Cu/SAPO-34 for NH 3 -SCR Reaction
- 2021
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Ingår i: Emission Control Science and Technology. - : Springer Science and Business Media LLC. - 2199-3629 .- 2199-3637. ; 7:3, s. 198-209
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Tidskriftsartikel (refereegranskat)abstract
- SAPO-34 were synthesized using three structure-directing agents (SDAs), i.e., tetraethylammonium hydroxide (TEAOH), triethylamine (TEA), and morpholine (MO). These SAPO-34 supports were used to prepare Cu/SAPO-34 catalysts via two different Cu-exchange methods: incipient wetness impregnation (IWI) and solid-state ion exchange (SSIE). The catalytic performance of Cu/SAPO-34(TEAOH, TEA, MO) catalysts prepared with IWI and SSIE before and after exposure to water vapor at 70 °C was systemically examined, and their deactivation behavior during low-temperature NH3-SCR reaction was studied. These catalysts were characterized by XRD, BET, ICP-SFMS, SEM/EDX, solid-state NMR, CO-DRIFTS, NO-DRIFTS, and H2-TPR. The various characterization findings for the Cu/SAPO-34 catalysts suggest that the distribution of different Cu2+ species and the mobility of Cu2+ in chabazite (CHA) structure are important for the low-temperature deactivation and regeneration behaviors of the Cu/SAPO-34(TEAOH, TEA, MO)-IWI and -SSIE during the NH3-SCR reaction. Thus, it has been determined that the choice of SDA and Cu-exchange method is vital to design of an efficient Cu/SAPO-34 catalyst that is highly active during a NH3-SCR reaction and has a high tolerance for the low-temperature deactivation caused by exposure to water vapor.
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| 16. |
- Xie, Kunpeng, 1985, et al.
(författare)
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Deactivation of Cu-SSZ-13 SCR catalysts by vapor-phase phosphorus exposure
- 2019
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 256
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Tidskriftsartikel (refereegranskat)abstract
- Phosphorus in vehicle exhaust is one of the typical derivatives from fuels and lubricant oils that cause irreversible deactivation of automotive catalysts. In this work, we investigate the deactivation of Cu-SSZ-13 by vapor-phase phosphorus poisoning (100 ppm H3PO4) under NH3-free lean conditions and NH3-SCR operating conditions. The poisoned monolith catalysts were characterized with XPS, ICP-SFMS, SEM-EDX mapping, and H2-TPR. The influence of phosphorus on catalytic performance (i.e. standard NH3-SCR, NH3 oxidation, NO oxidation, NH3 storage, and NO storage) was evaluated. Phosphorus is mainly stored in the form of metaphosphate in poisoned catalysts, and it possesses axial and radial gradients on catalyst washcoats. Phosphorus strongly affects the copper reduction property, as revealed by the shifts in copper reduction to higher temperature in H2-TPR experiments. Variations in phosphorus poisoning conditions are found to mainly impact the amounts of phosphorus captured and stored in the monolith catalysts. In order to elucidate the deactivation mechanism, the deactivation is correlated with the P/Cu ratio. The temperature shift for copper reduction significantly increases with the P/Cu ratio and levels at high Cu/P ratios. The deactivation degrees of NH3 oxidation and NO oxidation as a function of the P/Cu ratio follow the same trend as the copper reduction temperature. This is possibly due to the formation of copper phosphates in the large cages, which deactivates the copper sites for NH3 and NO oxidation. The deactivation for standard NH3-SCR, NH3 storage, and NO storage is proportional to the P/Cu ratio. The impact of phosphorus on NO storage is significantly stronger than on NH3 storage, indicating that greater contribution to deactivation is brought about by the decreased capacity of NO chemisorption.
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