Towards a realistic simulation model for NOx-storage catalyst dynamics

Schmeißer, Volker; Tuttlies, Ute; Eigenberger, Gerhart

doi:10.1007/s11244-007-0155-5

Cited by 13 publications

(27 citation statements)

References 6 publications

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“…at the end of the lean phase, turned out to be higher than in the stationary experiments (compare figures 2 and 7). This could be verified in simulation studies [5], where the rate constants of the stationary NO-oxidation kinetics had to be increased by a factor of about 3.5 to describe oxidation during lean/ rich-cycles sufficiently. This effect is even more pronounced at low temperatures when the conversion is not equilibrium limited.…”

Section: Resultsmentioning

confidence: 82%

“…Furthermore it can be seen that the NO xconcentration has an inhibiting effect on NO-oxidation, although this effect is only small for the Pt/Rh/Ce/Ba/ Al 2 O 3 -sample. This effect is mainly contributed to NO 2 rather than to NO, as shown in [5]. Small amounts of CO and C 3 H 6 in the lean feed show a clear influence as the NO 2 -formation is hindered as long as these reducing components are present.…”

Section: Resultsmentioning

confidence: 92%

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Experimental results concerning the role of Pt, Rh, Ba, Ce and Al2O3 on NO x -storage catalyst behaviour

et al. 2007

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NO x -storage catalysts (NSC) with varied washcoat compositions have been investigated experimentally under lean and rich conditions. Besides the fact that Ba and Rh are essential for NO x -storage and -reduction, it was observed that Ba accelerates the NO-reduction and decreases NO-oxidation kinetics. It also turned out to be the promoting species regarding water gas shift reaction. The results revealed kinetic inhibition effects by CO, C 3 H 6 and NO, being less pronounced with Ba in the washcoat. It is further shown that the cyclic NO x -conversion of the NSC is mainly determined by the processes in the regeneration phase.

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Section: Resultsmentioning

confidence: 82%

Section: Resultsmentioning

confidence: 92%

Experimental results concerning the role of Pt, Rh, Ba, Ce and Al2O3 on NO x -storage catalyst behaviour

et al. 2007

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“…Furthermore, experimental data has been fit quite well using just NO 2 trapping and ignoring NO trapping [25], both suggesting that a likely explanation for the observed trend is limited NO oxidation leading to limited NO 2 for trapping. Predictive NO oxidation models do exist [26][27][28][29], as do models for NSR catalyst cycling [30][31][32], the latter study having also predicted a maximum in nitrate concentration slightly downstream of the inlet. Two of the trapping portion of the models were adapted for this study [30,31]; adapted by inputting NO oxidation kinetics that include NO 2 inhibition [26], considering only NO 2 trapping kinetics with embedded diffusion resistance, and changing the catalyst details used as inputs to match those of the sample used in this study.…”

Section: Resultsmentioning

confidence: 94%

Spatially-Resolved Calorimetry: Using IR Thermography to Measure Temperature and Trapped NOX Distributions on a NOX Adsorber Catalyst

et al. 2008

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Spatial-and time-resolved temperature distributions over a Pt/Ba/Al 2 O 3 model NO X storage/reduction (NSR) catalyst were measured using infra-red thermography. The heat generated during regeneration was correlated to surface nitrate reduction, thereby revealing the concentration of surface nitrates at specific locations along the catalyst. The results demonstrate that there is more nitrate formation at upstream positions relative to downstream, or from front to back of the catalyst, with short trapping times. However, as more NO X was trapped on the catalyst during longer trapping times, it was found that the largest amount of NO X was trapped slightly downstream of the inlet, evolving to a local maximum in amount trapped. Applying infrared (IR) thermography to this system resulted in a spatially resolved calorimetry method via the correlation of temperature to the distribution of sorbed nitrate species along the catalyst.

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“…The reaction rates are based on Langmuir-Hinshelwood kinetics [15]. Under the assumption that adsorption and desorption are in equilibrium, the macrokinetic reaction rate can be derived from the microkinetic reaction steps [10].…”

Section: Macrokinetic Modelmentioning

confidence: 99%

Macro‐ and Microkinetic Simulation of Diesel Oxidation Catalyst: Effect of Aging, Noble Metal Loading and Platinum Oxidation

Hauff¹,

Boll²,

Tischer³

et al. 2013

Chemie Ingenieur Technik

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In automotive exhaust aftertreatment simulation, both macro-and microkinetic models are commonly used. In this contribution both models are applied for the simulation of diesel oxidation catalysts (Pt/c-Al 2 O 3 ) with different catalyst loading and degree of thermal aging. The study proves that the structure insensitive kinetics of the considered catalysts can be described with the same rate equations only by scaling the rate constants of the different reaction steps with the catalytically active Pt surface, which is accessible by CO adsorption or light-off measurements. In addition, NO oxidation is strongly influenced by a reversible, slow transformation of Pt into Pt-oxide. Catalyst aging 673give insight into the reaction network and coverage-dependent processes on the catalytic surface. For the oxidation of NO crucial information about the inhibition effect of NO can be obtained and used in the macrokinetic model. ExperimentalDOCs (Pt/c-Al 2 O 3 , 400 cpsi monolith) of a commercial catalyst supplier with three different platinum loadings have been investigated (Tab. 1). All catalysts underwent a hydrothermal pretreatment/aging in a furnace, for which the monoliths (diameter 75 mm, length 125 mm) were canned and flowed with 10 % water vapor in air. The catalysts DOC20, DOC60 and DOC120 (20, 60, 120 g ft -3 ) were pretreated for 16 h at 700°C. Two samples of DOC120 were hydrothermally aged for 16 h at 850°C (DOC120-850) and at 950°C (DOC120-950).After pretreatment/aging, catalyst slices (30 mm × 40 mm, one channel height: 1.4 mm) were taken from the center of the monolith for the kinetic measurements. The measurements were carried out in an isothermal flat bed reactor with five catalyst slices in a row [9, 10] under realistic flow conditions with synthetic exhaust gas and a space velocity of 40 000 h -1 . The measurement of the concentration profiles along the catalyst length was accomplished via lateral withdrawals after each slice. The experiment started with 5 min measurement versus the reactor end and continued for 1 min per lateral withdrawal. The synthetic exhaust gas consisted of 12 % O 2 , 7 % CO 2 , 10 % H 2 O and varying concentrations of C 3 H 6 (0 -1000 ppm), CO (0 -15 000 ppm) and NO (0 -500 ppm). Nitrogen was used for balance. The temperature was varied between 120 and 450°C.The specific platinum surface of all catalyst samples was determined by temperature programmed desorption of CO (CO-TPD). Before adsorption, the monolithic samples were reduced at 400°C with 10 % H 2 for 16 h. The temperature was set to 25°C and the catalyst was saturated with 10 % CO for 30 min followed by a temperature ramp (30 K min -1 ) to 500°C. The platinum dispersion D Pt and the specific platinum surface O Pt shown in Tab. 2 were calculated (Eqs. (1) and (2)) by the molar amount of desorbed CO, n TPD CO , and platinum deposited on the catalyst, n total Pt , assuming stoichio-metric adsorption (CO:Pt = 1:1) on the platinum surface. A detailed description of the CO-TPD procedure and experimental setup is given in [11].

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Towards a realistic simulation model for NOx-storage catalyst dynamics

Cited by 13 publications

References 6 publications

Experimental results concerning the role of Pt, Rh, Ba, Ce and Al2O3 on NO x -storage catalyst behaviour

Experimental results concerning the role of Pt, Rh, Ba, Ce and Al2O3 on NO x -storage catalyst behaviour

Spatially-Resolved Calorimetry: Using IR Thermography to Measure Temperature and Trapped NOX Distributions on a NOX Adsorber Catalyst

Macro‐ and Microkinetic Simulation of Diesel Oxidation Catalyst: Effect of Aging, Noble Metal Loading and Platinum Oxidation

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