| 1. |
- Lundberg, Björn, 1982, et al.
(författare)
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DOC modeling combining kinetics and mass transfer using inert washcoat layers
- 2016
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 191, s. 116-129
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to develop a kinetic and transport model for diesel oxidation catalysts (DOC) with a satisfactory compromise between accuracy and computational demands for robust simulation of transient full-scale operation. Specifically the model accounts for surface concentrations of key species needed to capture transient features for typical lean exhaust conditions. In addition, the model accounts for transport limitations and distinguish them from reaction kinetics as well as apparent NO oxidation inhibition effects due to reactions. To achieve this, lab scale experiments were performed with DOCs with different platinum loadings and three different washcoat configurations of which two had an inert top layer. Both kinetic parameters for a detailed kinetic model and effective diffusivities were optimized for the experimental data using a single channel catalyst model. The experiments showed a clear effect of increased transport resistance for propene and CO and also that NO2 plays an important role as an oxidizing agent for preferentially CO at low temperature (
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| 2. |
- Lundberg, Björn, 1982, et al.
(författare)
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Model-based experimental screening for DOC parameter estimation
- 2015
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Ingår i: Computers and Chemical Engineering. - : Elsevier BV. - 0098-1354. ; 74, s. 144-157
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Tidskriftsartikel (refereegranskat)abstract
- In the current study a parameter estimation method based on data screening by sensitivity analysis is presented. The method applied Multivariate Data Analysis (MVDA) on a large transient data set to select different subsets on which parameters estimation was performed. The subset was continuously updated as the parameter values developed using Principal Component Analysis (PCA) and D-optimal onion design. The measurement data was taken from a Diesel Oxidation Catalyst (DOC) connected to a full scale engine rig and both kinetic and mass transport parameters were estimated. The methodology was compared to a conventional parameter estimation method and it was concluded that the proposed method achieved a 32% lower residual sum of squares but also that it displayed less tendencies to converge to a local minima. The computational time was however significantly longer for the evaluated method.
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| 3. |
- Lundberg, Björn, 1982, et al.
(författare)
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New Methodology for Transient Engine Rig Experiments for Efficient Parameter Estimation
- 2013
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Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 6:4, s. 1995-2003
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Tidskriftsartikel (refereegranskat)abstract
- Introduction The diesel oxidation catalyst (DOC) is a well established technology to reduce CO and hydrocarbon (HC) emissions from diesel engines. Strengthened emission standards have made the importance of the DOC even greater in recent years since it plays an indispensible role in enhancing the performance of diesel particulate filters (DPF) and selective catalytic reduction (SCR) by utilization of NO oxidation to NO2. Therefore correct prediction of the DOC performance is very important for simulations of the entire aftertreatment system. When performing kinetic parameter estimation, laboratory scale experimental data is generally used. In laboratory scale it is possible to use essentially any combination of exhaust gas composition and temperature which makes it possible to estimate parameters over a wide range of conditions. However the applicability of these parameters in full scale models is often limited. Parameter estimation on full scale engine rig experiments on the other hand is limited by the exhaust compositions that are possible for the engine to produce. As a result, the fraction of CO is closely linked to the fraction of hydrocarbons and the fraction of NO is closely linked to the fraction of NO2. When switching between two engine operation points it generally takes several minutes before the properties of the emissions have stabilized. This does not only make the experiments time consuming, but it also complicates the transient modeling of the DOC since the changes in inlet properties are far from ideal step functions. In this study an experimental set-up is presented that makes it possible to change the inlet properties of the DOC without changing engine load point which results in much faster transients. The method also makes it possible to change the fraction of NO2 independently of the NO fraction. Method To achieve more controlled and faster changes in the inlet to the catalyst an extra DOC (DOC1) with the possibility for bypass flow and an SCR with urea injection are mounted before the catalyst. The fraction of exhaust gas flow through DOC1 allows variation in the conversion of HC and CO to CO2 and the conversion of NO to NO2. By injecting different amounts of urea the conversion of NO2 and NO to N2 is controlled. The SCR also makes it possible to obtain an inlet composition to the DOC that contains NO2 but is free of NO. Fast changes in inlet conditions are in other words possible and it is also possible to achieve compositions not achievable by only controlling the operation of the engine. Experiments have been performed at several engine conditions and using catalysts with different noble metal loading, lengths and washcoat thicknesses. To achieve high HC and CO concentrations the engine was tuned to run with late fuel injection. Significance A method to carry out engine rig experiments with a wider range of emission conditions makes it possible to more efficiently retune model parameters for a full-scale catalyst from literature data. This should result in faster model development which is of great importance in exhaust gas aftertreatment.
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| 4. |
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| 5. |
- Lundberg, Björn, 1982, et al.
(författare)
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Parameter Estimation of a DOC from Engine Rig Experiments with a Discretized Catalyst Washcoat Model
- 2014
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Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 7:2, s. 1093-1112
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Tidskriftsartikel (refereegranskat)abstract
- Parameter tuning was performed against data from a full scale engine rig with a Diesel Oxidation Catalysts (DOC). Several different catalyst configurations were used with varying Pt loading, washcoat thickness and volume. To illustrate the interplay between kinetics and mass transport, engine operating points were chosen with a wide variation in variables (inlet conditions) and both transient and stationary operation was used. A catalyst model was developed where the catalyst washcoat was discretized as tanks in series both radially and axially. Three different model configurations were used for parameter tuning, evaluating three different approaches to modeling of internal transport resistance. It was concluded that for a catalyst model with internal transport resistance the best fit could be achieved if some parameters affecting the internal mass transport were tuned in addition to the kinetic parameters. However it was also shown that a model with negligible internal transport resistance still could obtain a good fit since kinetic parameters could compensate for transport limitations. This highlighted the inherent difficulties using kinetic models with high parameter correlation and also showed the importance of using a kinetic model with a structure that is capable of describing exclusively intrinsic kinetics.
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| 6. |
- Lundström, Andreas, 1980, et al.
(författare)
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Modelling of urea gas phase thermolysis and theoretical details on urea evaporation
- 2011
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. - : SAGE Publications. - 2041-2991 .- 0954-4070. ; 225:10, s. 1392-1398
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Tidskriftsartikel (refereegranskat)abstract
- A model study of droplet decomposition of a urea–water solution (UWS) for selective catalytic reduction applications (SCR) has been undertaken. A new vapour pressure equation for urea has been adopted to predict the rate of urea evaporation. The vapour pressure above liquid urea is obtained by extrapolating the vapour pressure above solid urea. Gas phase decomposition of urea into ammonia and isocyanic acid is further assumed to be fast, dictating the boundary conditions for the evaporation process. The rate of UWS evaporation is compared to recently published data and shows good agreement. A set of Antoine parameters was fitted to the derived vapour pressure to facilitate future simulations.
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| 7. |
- Acke, Filip, 1968, et al.
(författare)
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Influence of the platinum-support interaction on the direct reduction of NOx under lean conditions
- 1998
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 116, s. 285-294
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Tidskriftsartikel (refereegranskat)abstract
- Catalysts containing Pt supported on SiC, Al2O3 and ZSM-5 were prepared and studied for NOx reduction by C3H6 in Oz excess under transient (temperature ramps) and steady-state conditions. The maximum NOx reduction activity in the heating ramp experiments was similar for Pt/SiC and Pt/ZSM-5, while Pt/Al2O3 showed higher maximum activity. Both N-2 and N2O formation was observed for all catalysts, although the respective amounts varied with the investigated system. Highest Nz selectivity was observed for Pt/Al2O3. When the NOx reduction activity was studied under steady-state conditions the activity of Pt/Al2O3 decreased substantially (mainly due to a loss in N-2 production). Pt/ZSM-5 became somewhat more selective towards Na production whereas the activity and selectivity of Pt/SiC remained at about the same values as far the heating ramp experiments. Adsorbed species on the surface of the different catalysts were investigated using in-situ FTIR in order to obtain information about the reaction mechanisms. The adsorption of species on Pt/SiC was negligible, while a number of absorption bands were observed for Pt/Al2O3 (N and C containing species, and -NCO) and Pt/ZSM-5 (HC).
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| 8. |
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| 9. |
- Acke, Filip, 1968, et al.
(författare)
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Selective reduction of NO by HNCO over Pt promoted Al2O3
- 1998
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 179:2, s. 528-536
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Tidskriftsartikel (refereegranskat)abstract
- The activity of Pt supported on gamma-Al2O3 towards HNCO oxidation and reduction of NO by HNCO under oxygen excess is examined under transient conditions (temperature ramps between 100 and 500 degrees C). Formation of N-2, N2O, NO, and NO2 is observed. Isotope labelled (NO)-N-15 is used to show the scrambling of nitrogens in N-2 ((NN)-N-14-N-15) and N2O ((NNO)-N-14-N-15). Adsorbed species on the surface are characterised by in-situ FTIR spectroscopy in order to obtain information on reaction intermediates. Adsorbed NNx species are discussed as important intermediates in the N-2 and N2O formation. The absence of Pt results in a delay in HNCO ignition and only a small N2O formation is observed.
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| 10. |
- Amberntsson, Annika, 1974, et al.
(författare)
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Sulphur dioxide deactivation of NOx storage catalysts
- 1999
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 126, s. 317-324
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Tidskriftsartikel (refereegranskat)abstract
- The influence of sulphur dioxide on the NOx storage performance of a Pt-Rh/BaO/Al2O3 model catalyst has been investigated. Addition of 2.5-25 vol.-ppm SO2 to a synthetic lean-burn exhaust, containing NO, C3H6, O2 and Ar, caused deactivation of the NOx storage function of the catalyst. The rate of deactivation was found to be proportional to the exposure of SO2. This effect is seen for temperatures between 250 and 450 degrees C. Together with in situ FTIR measurements, this leads to the conclusion that sulphur accumulates in the NOx storage component of the catalyst during the exposure. Furthermore, SO2 also inhibits the oxidation capacity of the catalyst during lean periods as is observed by a decreased NO oxidation activity. The presence of SO2 also reduces the reduction capacity of the catalyst under rich periods, which leads to an increased N2O formation and a decreased NO conversion.
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| 11. |
- Fridell, Erik, 1963, et al.
(författare)
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Investigation of NOx storage catalysts
- 1997
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Ingår i: 4th International Congress on Catalysis and Automotive Pollution Control (CAPoC4) in Brussels, Belgium, April 9-11, 1997.
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Konferensbidrag (refereegranskat)
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| 12. |
- Fridell, Erik, 1963, et al.
(författare)
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Investigations of NOx storage catalysts
- 1998
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 116, s. 537-547
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Tidskriftsartikel (refereegranskat)abstract
- NOx storage catalysts are used to reduce nitrogen oxides from lean-burn vehicles. The nitrogen oxides are stored in the catalyst during lean conditions and subsequently released and reduced during short periods of rich conditions. In the present study, we systematically investigate the sequence of elementary steps in the NOx reduction cycle, and the extent to which these steps influence the maximum NOx, reduction potential of the catalyst. As a model system, we use barium oxide as the NOx, storing compound in a Pt/Rh/Al2O3 system. Kinetics of NO oxidation, NO and NO2 adsorption, NO and NO2 release and reduction are studied under controlled conditions with systematic variations of temperature, gas composition, and storing/release times. The transient experiments comprise a storing phase using a lean NO/C3H6/O2/N2 gas mixture, and a regenerating phase where the O2 now is turned off. Experimentally, a significant amount of NOx is found to be stored in the Ba-containing material. A maximum in NOx storage is observed around 380 degrees C. For most of the experiments, there are clear NO and NO2 desorption peaks upon switching from the storing to the regeneration phase. TPD studies of NO and NO2 reveal a significant difference between prereduced and pre-oxidised samples where the former produce predominantly N2 and N2O at around 200 degrees C while NO and O2 desorb from the latter around 500 degrees C. In situ FTIR spectra show nitrate peaks in the region 1300-1400 cm(-1) when NOx is stored under lean conditions.
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| 13. |
- Fridell, Erik, 1963, et al.
(författare)
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Model studies of NOx storage
- 2001
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Ingår i: ENVICAT2001, Amolfi, Italy, May 2-6, 2001.
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Konferensbidrag (refereegranskat)
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| 14. |
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| 15. |
- Fridell, Erik, 1963, et al.
(författare)
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Model studies of NOx storage and sulphur deactivation of NOx storage catalysts
- 2001
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Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 16-17:1-4, s. 133-137
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Tidskriftsartikel (refereegranskat)abstract
- The storage of NOx under lean conditions in model NOx storage catalysts as well as the deactivation by sulphur have been studied. We find that NO2 plays an important role in the storage mechanism as an oxidising agent. Two different mechanisms for this are discussed: the formation of surface peroxides and the oxidation of nitrites to nitrates, FTIR studies show that NOx is stored as surface nitrates, The sulphur deactivation is found to be more severe when SO2 is added during the rich phase than when SO2 is added during the lean period. FTIR shows the formation of bulk sulphates both under lean and rich conditions.
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| 16. |
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| 17. |
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| 18. |
- Fridell, Erik, 1963, et al.
(författare)
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NOx storage in barium-containing catalysts
- 1999
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 183:2, s. 196-209
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Tidskriftsartikel (refereegranskat)abstract
- The effect of key parameters on the characteristics of barium oxide-based NOx storage catalysts was systematically investigated. Model Pt/BaO/Al2O3, BaO/Al2O3, Pt–Rh/Al2O3, and Pt–Rh/BaO/Al2O3 catalysts were prepared and evaluated with respect to NOx storage capacity using transient flow reactor studies, temperature-programmed desorption studies (TPD), and in situ Fourier transform infrared (FTIR) absorption spectroscopy. The influence of temperature, storage and regeneration times, NOx source (NO or NO2), oxygen concentration, reducing agent (C3H6, C3H8, CO, or H2), and carbon dioxide concentration onNOx storage capacity was studied. Significant amounts of NOx were found to be stored in the catalysts containing both barium oxide and noble metals. For these catalysts the following observations were made: (1) maximum NOx storage was observed at about 380C;(2) around this temperature no significant differences between NO and NO2 on NOx storage capacity could be observed;(3) a slow increase in stored NOx could be observed with increasing oxygen concentration during the lean phase;(4) significant NOx desorption peaks, mainly of NO, were observed immediately after the switch from lean to rich conditions; and (5) at about 380±C the in situ FTIR spectra show characteristic nitrate peaks in the region 1300–1400 cm¡1 when NOx was stored under lean conditions and isocyanate peaks around 2230 cm-1 when the catalysts were regenerated under rich conditions in the presence of hydrocarbons. The step leading to stored NOx is believed to involve NO2 and the presence of atomic oxygen. During the rich period, the noble metal surfaces are probably reduced, leading to breakthrough peaks when NO desorbs.
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| 19. |
- Fridell, Erik, 1963, et al.
(författare)
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The Mechanism for NOx Storage
- 2000
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Ingår i: Catalysis Letters. - 1572-879X .- 1011-372X. ; 66:1-2, s. 71-74
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms for storing of NOx in platinum-barium-alumina catalysts during lean-rich transients are investigated. Oxidation of NO to NO2 is found to be an important step. NO2 is found to be important for oxidation of the catalyst or of nitrites to form nitrates. NOx is then stored in the form of surface nitrates. FTIR studies show no formation of bulk nitrates in these experiments.
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| 20. |
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| 21. |
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| 22. |
- Olsson, Louise, 1974, et al.
(författare)
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A kinetic study of oxygen adsorption/desorption and NO oxidation over Pt/Al2O3 catalysts
- 1999
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Ingår i: Journal of Physical Chemistry B Materials. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 103:47, s. 10433-10439
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Tidskriftsartikel (refereegranskat)abstract
- Laboratory tests and kinetic modeling were carried out in order to provide kinetic input data to a systematic investigation of the mechanism of nitrogen oxides (NO,) storage in catalysts used for lean-burn engines. In particular, we present a kinetic model of the NO oxidation to NO2 over a Pt/Al2O3 model catalyst for the temperature range 250-450 degrees C. Since the oxygen behavior at atmospheric pressure is critical for such a model, we have also studied the adsorption/desorption of oxygen by temperature-programmed desorption (TPD) experiments. The experiments show that oxygen starts to desorb at about 300 degrees C. Furthermore, the NO oxidation was studied in a temperature ramp with NO and oxygen in the gas feed. The data from this experiment and the above-determined values for the oxygen adsorption/desorption were used to construct a kinetic model for the NO oxidation. Finally, the model was validated with some transient experiments with either NO or NO2 and different oxygen concentrations in the gas feed. We found a good agreement between these experiments and the model.
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| 23. |
- Skoglundh, Magnus, 1965, et al.
(författare)
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Model studies of NOx storage catalysts
- 2000
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Ingår i: 2000 International Chemical Congress of Pacific Basin Societies (PACIFICHEM’2000) in Honolulu, Hawaii, USA, December 14-19, 2000..
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Konferensbidrag (refereegranskat)
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| 24. |
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| 25. |
- Westerberg, Björn, 1962
(författare)
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FTIR Studies and Kinetic Modelling of NOX Reduction and NOX Storage
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- FTIR spectroscopy and kinetic modelling have been used to study catalysts for NOX reduction and NOX storage. For Pt/Al2O3 exposed to NO, oxygen and propene IR-bands associated with nitrates, acetate, formate, carbonates and isocyanate were observed. Experiments with NO, oxygen and HNCO showed that isocyanate is an intermediate for reduction of NOX. For Pt/BaO/Al2O3 exposed to NO, propene and excess oxygen mainly IR-bands associated with nitrates and acetate were observed. During hydrocarbon excess conditions the sizes of these bands decreased and a band associated with isocyanate became apparent. The adsorption and desorption of oxygen and NO or NO2 at different temperatures on Al2O3, BaO/Al2O3, Pt/Al2O3, and Pt/BaO/Al2O3 were studied with FTIR spectroscopy. For Al2O3 and BaO/Al2O3 exposed to NO and oxygen small nitrite and hyponitrite bands were observed. When exposed to NO2 and oxygen large nitrate-bands were observed. For Pt/Al2O3 and Pt/BaO/Al2O3 exposed to NO and oxygen small nitrite and hyponitrite-bands were observed at 100 and 150ºC. At 200ºC and at higher temperatures large nitrate-bands were formed. It was found that Pt influences the stability of the nitrates via the NO2 decomposition reaction. The deactivation of Pt/BaO/Al2O3 by SO2 was studied with FTIR spectroscopy. After exposures to SO2 and oxygen at 350ºC bands associated with surface and bulk sulphates were observed. Treatment in hydrogen reduced the size of these bands and the bands associated with surface sulphates were more readily reduced. The oxidation of NO on Pt/Al2O3 was modelled with an Eley-Rideal mechanism. A good agreement between model and experiments was obtained. The storage of NOX on Al2O3 was modelled. A mechanism with gas phase N2O3, N2O4 and N2O5 as important intermediates could accurately describe the storage and release of NO2 in presence and in absence of NO. A high temperature catalyst for diesel exhaust after-treatment was modelled. A mechanism with nitrate, partially oxidised hydrocarbon and isocyanate as important intermediates was used. The model showed reasonable agreement with experimental data for CO, NOX and NO2. There was however a lack of fit for hydrocarbon, which was suspected to be related to the heterogeneity of diesel fuel.
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| 26. |
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| 27. |
- Österlund, Lars, 1967, et al.
(författare)
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Model studies of NOx storage
- 1999
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Ingår i: 8th European Conference on Applications of Surface and Interface Analysis (ECASIA’99) in Sevilla, Spain, October, 4-8, 1999.
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Konferensbidrag (refereegranskat)
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