Abatement of pollutant emissions over platinum-containing catalytic converters of lean operated engines is studied. Several close-to-production model catalysts with varying platinum loading and hydrothermal aging procedures are characterized by BET, HR-SEM, HR-TEM, and CO-TPD. Pollutant conversion is numerically investigated in an isothermal flat bed reactor using varying lean exhaust-gas mixtures and temperatures. The performance of the monolithic catalysts is modeled by a two-dimensional flow field description of a single channel coupled with models for washcoat diffusion and multistep reaction mechanisms. An optimizing procedure is presented which allows adaption of kinetic parameters for slightly different catalysts. The catalytic active surface area of the catalyst determined by CO-TPD can serve as parameter to model the varying noble metal loading and consequences of hydrothermal aging without any adaption of the kinetic data included in the reaction mechanism.

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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