| 1. |
- 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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| 2. |
- Arora, Prakhar, 1987, et al.
(författare)
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Investigating the effect of Fe as a poison for catalytic HDO over sulfided NiMo alumina catalysts
- 2018
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 227, s. 240-251
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Tidskriftsartikel (refereegranskat)abstract
- The effect of iron (Fe) as poison present in renewable feeds was studied during hydrodeoxygenation (HDO) overmolybdenum based sulfided catalysts. The study was carried out at 6 MPa and 325 °C in batch reaction conditions. Different concentrations of Fe in the feed were tested over MoS2/Al2O3 and NiMoS/Al2O3. A notable drop in activity for the conversion of oxygenates was observed for both catalyst systems with an increased concentration of Fe in the feed. However, the changes in selectivity of products was opposite for unpromoted and Nipromoted catalysts. In the case of the NiMoS catalyst, at higher Fe concentration, the decarbonated product (C17 hydrocarbons) decreased while the direct hydrodeoxygenation product (C18 hydrocarbons)increased. On the contrary, for the base catalyst (MoS2), there was a decrease in the yield of direct hydrodeoxygenation (C18 hydrocarbons) products and an increase in yield of decarbonated products (C17 hydrocarbons). These sulfided catalysts have different sites for these two different reaction routes and they interacted differently with Fe during the deactivation process. With surface deposition of Fe, the ability of these catalysts to create active sites i.e. via sulfur vacancies deteriorated. TEM-EDX results suggested that the effect of Ni as a promoter for the decarbonation route was nullified and a resultant FeMo phase explains the drop in activity and change in selectivity.
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| 3. |
- De Abreu Goes, Jesus, 1989, et al.
(författare)
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Effects of Feed Gas Composition on Fresh and Aged TWC-Coated GPFs Loaded with Real Soot
- 2020
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 59:23, s. 10790-10803
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Tidskriftsartikel (refereegranskat)abstract
- Catalyzed gasoline particulate filters (cGPFs) are one of the most promising technologies to meet future stringent gaseous and particulate emission limits for gasoline-powered vehicles. The successful adoption of this technology relies on several important properties including high filtration efficiency, low back-pressure, high conversion efficiency, and great durability compliance. Particularly in this work, the conversion efficiency and durability of model cGPF catalysts were studied under different feed temperatures and multicomponent feed gas mixtures. The samples consisted of soot-free and real soot-loaded GPFs coated with noble metals supported on alumina and Ce-Zr mixed oxides. Prior to testing, the samples were subjected to diverse hydrothermal aging conditions. Some physicochemical characterization techniques, including scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and nitrogen physisorption, were employed to study the fundamental relations between the state of the samples and their catalytic properties. The results showed that the introduction of soot appeared to have both a positive and negative effect on the catalyst activity. The catalyst surface is masked by the introduction of soot, blocking active sites and inhibiting species conversion. At the same time, the exothermicity of the soot oxidation reaction increases the catalyst temperature, reducing the light-off temperature, for the severely aged samples. Besides the presence of soot, the catalyst aging considerably influences the reactions over cGPFs. In particular, the conversions of ethylene and toluene were more affected by the catalyst aging than CO, which became even worse in the presence of NO in the feed gas. The formation of side products (NH3 and N2O) over the cGPFs was also examined under diverse practical conditions.
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| 4. |
- Feizie Ilmasani, Rojin, 1989, et al.
(författare)
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Influencing the NOx Stability by Metal Oxide Addition to Pd/BEA for Passive NOx Adsorbers
- 2020
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 59:21, s. 9830-9840
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Tidskriftsartikel (refereegranskat)abstract
- Passive NOx adsorption performance was investigated for Pd-based BEA zeolite as a reference sample along with ceria, zirconium, and lanthanum as different promoters. The La-promoted sample showed favorable NOx desorption behavior regarding greater quantities of NOx release at temperatures higher than 200 degrees C. The study was therefore mainly focused on the La-promoted sample and Pd/BEA, since the largest effect was seen using La as a promoter. The effect of water and hydrogen pretreatments for passive NOx adsorption (PNA) processes was therefore studied for La-Pd/BEA and compared with that for pure Pd/BEA. It was shown that the presence of water reduces the NOx desorption at lower temperature. Hydrogen pretreatment decreases the NOx uptake and shifts the adsorption and desorption temperatures to higher values. Interestingly, the La-Pd/BEA sample was less sensitive to H-2 pretreatment. Temperature-programmed oxidation (TPO) and X-ray photoelectron spectroscopy (XPS) results indicated the presence of more stable Pd oxide sites for La-Pd/BEA. Furthermore, Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis suggested that NO is adsorbed with stronger and more stable bonds in the form of nitrates compared with the Pd/BEA reference sample.
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| 5. |
- Friberg, Ida, 1990, et al.
(författare)
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Structure and performance of zeolite supported Pd for complete methane oxidation
- 2021
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 382, s. 3-12
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Tidskriftsartikel (refereegranskat)abstract
- The influence of zeolite support materials and their impact on CH oxidation activity was studied utilizing Pd supported on H-beta and H-SSZ-13. A correlation between CH oxidation activity, Si/Al ratio (SAR), the type of zeolite framework, reduction-oxidation behaviour, and Pd species present was found by combining catalytic activity measurements with a variety of characterization methods (operando XAS, NH -TPD, SAXS, STEM and NaCl titration). Operando XAS analysis indicated that catalysts with high CH oxidation activity experienced rapid transitions between metallic- and oxidized-Pd states when switching between rich and lean conditions. This behaviour was exhibited by catalysts with dispersed Pd particles. By contrast, the formation of ion-exchanged Pd and large Pd particles appeared to have a detrimental effect on the oxidation-reduction behaviour and the conversion of CH . The formation of ion-exchanged Pd and large Pd particles was limited by using a highly siliceous beta zeolite support with a low capacity for cation exchange. The same effect was also found using a small-pore SSZ-13 zeolite due to the lower mobility of Pd species. It was found that the zeolite support material should be carefully selected so that the well-dispersed Pd particles remain, and the formation of ion-exchanged Pd is minimized. 4 4 3 4 4 2+ 2+ 2+
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| 6. |
- Ho, Hoang Phuoc, 1983, et al.
(författare)
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The role of Pd-Pt Interactions in the Oxidation and Sulfur Resistance of Bimetallic Pd-Pt/γ-Al2O3 Diesel Oxidation Catalysts
- 2021
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 60:18, s. 6596-6612
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Tidskriftsartikel (refereegranskat)abstract
- Diesel oxidation catalysts (DOC) were investigated for oxidation activity, NO conversion stability, and sulfur poisoning/regeneration on Pd/Al2O3, Pt/Al2O3, and Pd-Pt/Al2O3 catalysts. The Pd/Al2O3 catalyst was more active for CO and hydrocarbon (C3H6 and C3H8) oxidation, while the Pt/Al2O3 catalyst efficiently oxidized NO. The formation of a Pd-Pt alloy in the Pd-Pt/Al2O3 catalyst maintained Pd in a more reduced phase, resulting in the superior activity of this catalyst for the oxidation of CO, C3H6, and NO in comparison with its monometallic counterparts. The Pd-Pt alloy not only provided more low-temperature activity but also retained the stability of NO oxidation. The Pd-Pt alloy also favored the spillover of SO2 to the alumina support, resulting in significantly higher adsorption capacity of the Pd-Pt/Al2O3 catalyst, extensively prolonging its lifetime. However, the stable sulfates on Pd-Pt/Al2O3 made it difficult to completely regenerate the catalyst. The bimetallic sample showed higher activity for CO, C3H8, and C3H6 after sulfur poisoning and regeneration.
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| 7. |
- Jonsson, Rasmus, 1989, et al.
(författare)
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Gas-phase phosphorous poisoning of a Pt/Ba/Al2O3 NOx storage catalyst
- 2018
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Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 8:4
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Tidskriftsartikel (refereegranskat)abstract
- The effect of phosphorous exposure on the NO x storage capacity of a Pt/Ba/Al 2 O 3 catalyst coated on a ceramic monolith substrate has been studied. The catalyst was exposed to phosphorous by evaporating phosphoric acid in presence of H 2 O and O 2 . The NOx storage capacity was measured before and after the phosphorus exposure and a significant loss of the NO x storage capacity was detected after phosphorous exposure. The phosphorous poisoned samples were characterized by X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM), N 2 -physisorption and inductive coupled plasma atomic emission spectroscopy (ICP-AES). All characterization methods showed an axial distribution of phosphorous ranging from the inlet to the outlet of the coated monolith samples with a higher concentration at the inlet of the samples. Elemental analysis, using ICP-AES, confirmed this distribution of phosphorous on the catalyst surface. The specific surface area and pore volume were significantly lower at the inlet section of the monolith where the phosphorous concentration was higher, and higher at the outlet where the phosphorous concentration was lower. The results from the XPS and scanning electron microscopy (SEM)-energy dispersive X-ray (EDX) analyses showed higher accumulation of phosphorus towards the surface of the catalyst at the inlet of the monolith and the phosphorus was to a large extent present in the form of P 4 O 10 . However, in the middle section of the monolith, the XPS analysis revealed the presence of more metaphosphate (PO 3 – ). Moreover, the SEM-EDX analysis showed that the phosphorous to higher extent had diffused into the washcoat and was less accumulated at the surface close to the outlet of the sample
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| 8. |
- Jonsson, Rasmus, 1989, et al.
(författare)
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Zeolite beta doped with La, Fe, and Pd as a hydrocarbon trap
- 2020
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Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 10:2
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Tidskriftsartikel (refereegranskat)abstract
- Hydrocarbon trapping is a technique of great relevance, since a substantial part of hydrocarbon emissions from engines are released from engines before the catalyst has reached the temperature for efficient conversion of the hydrocarbons. In this work, the influence of doping zeolite beta (BEA) with Fe, Pd, and La on the storage and release of propene and toluene is studied. Five monolith samples were prepared; Fe/BEA, La/BEA, Pd/BEA, Pd/Fe/BEA, and Pd/La/BEA using incipient wetness impregnation, and the corresponding powder samples were used for catalyst characterization by Inductively coupled plasma sector field mass spectrometry (ICP-SFMS), Temperature-programmed oxidation (TPO), X-ray photoelectron spectroscopy (XPS) and Scanning transmission electron microscopy with Energy dispersive X-ray analysis (STEM-EDX). The hydrocarbon trapping ability of the samples was quantified using Temperature-programmed desorption (TPD) of propene and toluene, and in situ Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results from the TPD experiments show that the addition of Pd and La to the zeolite affected the release patterns of the stored hydrocarbons on the trapping material in a positive way. The in situ DRIFTS results indicate that these elements provide H-BEA with additional sites for the storage of hydrocarbons. Furthermore, EDX-mapping showed that the La and Pd are located in close connection.
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| 9. |
- Trandafilovic, Lidija, 1975, et al.
(författare)
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A kinetic model for SCR coated particulate filters: Effect of ammonia-soot interactions
- 2019
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 241, s. 66-80
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Tidskriftsartikel (refereegranskat)abstract
- SCR coated filters have recently been introduced. These combine soot capture through diesel particulate filters (DPF) and NOxremoval through ammonia selective catalytic reduction (NH3SCR). This study investigates the impact of soot on the reactions being important for the SCR process on Cu/SSZ-13, as well as the impact of different gases on soot oxidation using flow reactor measurements. A limited impact of soot on the SCR reactions and a clear inhibiting effect of NH3on soot oxidation, is found. Ammonia TPD, in-situ DRIFT, and XPS experiments are used to investigate the interaction between soot and ammonia. Amines/amides are found on the soot when exposed to NH3and H2O. The results are used to develop a kinetic model for soot oxidation over DPF and a soot coated Cu/SSZ-13 catalyst using diesel soot generated from an engine bench. It is found that it is important to incorporate a random pore model and a free edge site mechanism through which ammonia block these free edge carbons. The model describes well soot oxidation in the presence of NH3over DPF, as well as soot oxidation and the SCR mechanism over soot loaded Cu/SSZ-13.
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| 10. |
- Woo, Jung Won, 1980, et al.
(författare)
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Effect of various structure directing agents (SDAs) on low-temperature deactivation of Cu/SAPO-34 during NH3-SCR reaction
- 2018
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 8:12, s. 3090-3106
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Tidskriftsartikel (refereegranskat)abstract
- Cu/SAPO-34 and Cu/SSZ-13 having chabazite structure (CHA) have attracted significant attention because of their high activity and N2selectivity during SCR reaction as well as superior resistance to hydrocarbon poisoning. Cu/SAPO-34 has shown better hydrothermal durability than Cu/SSZ-13 at high temperature. However, we have observed earlier that Cu/SAPO-34 prepared using morpholine as a structure directing agent (SDA) deteriorated under water exposure at low temperature, where the NOxconversion activity decreased from 87% to 6% after 9 h of low temperature exposure. In this study, Cu/SAPO-34 catalysts prepared using three different SDAs, i.e., morpholine (MO), triethylamine (TEA), and tetraethylammonium hydroxide (TEAOH), were prepared by the incipient wetness impregnation (IWI) method. A commercially purchased SAPO-34 (SAPO-34(ACS)) was also used for comparison purposes. After low temperature water deactivation, Cu/SAPO-34(TEA) and (TEAOH) mostly recovered their activities while Cu/SAPO-34(MO) and (ACS) only regained part of their activities after regeneration tests under a series of experimental conditions for the NH3-SCR reaction. Solid-state MAS NMR was employed to study the impact of SDAs on the coordination of Al, P, and Si in the SAPO-34 supports and Cu/SAPO-34 catalysts. CO-DRIFTS, NO-DRIFTS, and H2-TPR employed in this study collectively propose the presence of two different Cu locations in Cu/SAPO-34(MO, TEA, TEAOH, and ACS). It is suggested that the concentrations of Cu in two distinct locations within Cu/SAPO-34 catalysts characterized by CO-DRIFTS, NO-DRIFTS, and H2-TPR studies are significantly influenced by the choice of SDA, which will be important for understanding the deactivation mechanism of Cu/SAPO-34 catalysts during low temperature NH3-SCR reaction.
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