Jma Jan Harmsen

Kinetic modeling for wet air oxidation of formic acid on a carbon supported platinum catalyst

A study of the intrinsic kinetics of the oxidation of formic acid over a 1% Pt/C catalyst has been performed, at oxygen concentrations in water varying from 0.6 to 2.8 mol m−3 and at formic acid concentrations varying from 30 to 400 mol m−3. Experiments were performed in a continuous-flow stirred slurry reactor. To avoid mass transfer limitation of oxygen, a temperature interval from 282 to 293 K and a total pressure in the reactor of 0.6 MPa has been used. The pH interval of the experiments ranged from 1.1 to 13.0. Single response non-linear regression has been used to fit the parameters for a kinetic model. The proposed model can predict the steady-state disappearance rate of formic acid, as a function of the oxygen concentration, the formic acid concentration, the temperature and of the pH. Electrochemical experiments have been carried out for a better understanding of the pH effect on the formic acid oxidation.

Acetylene and carbon monoxide oxidation over a Pt/Rh/CeO2/γ-Al2O3 automotive exhaust gas catalyst : kinetic modelling of transient experiments

The transient kinetics of acetylene (C2H2) conversion by oxygen over a commercial Pt/Rh/CeO2/γ-Al2O3 three-way catalyst have been modelled. Experiments to validate the model were carried out in a fixed-bed reactor with two separate inlets, enabling alternate feeding of acetylene and oxygen. Frequencies of feed composition cycling up to were applied. The experimental conditions resemble the cold-start period of an Otto engine. Two types of adsorbed acetylene species seem to exist. A selective catalyst deactivation for oxygen adsorption, due to deposition of carbonaceous deposits, was found. Ceria proved to have a significant influence on the acetylene oxidation. A kinetic model was developed for the conversion of acetylene to carbon monoxide, based on elementary reaction steps. This model was combined with the published kinetics for transient carbon monoxide oxidation to carbon dioxide over the same catalyst (Nibbelke, R. H., Chapman, M. A. J., Hoebink, J. H. B. J., & Marin, G. B. (1997). Kinetic study of the CO oxidation over Pt/V-Al2O3 and Pt/Rh/ CeO2/γ−Al2O3 in the presence of H2O and CO2. Journal of Catalysis, 171, 358–373.), in order to describe the total oxidation of acetylene quantitatively. The combined model is able to describe the results of the transient experiments on simultaneous acetylene and carbon monoxide oxidation. During a transient, both acetylene and carbon monoxide react mainly in a front moving through the reactor, carbon monoxide hardly influencing the acetylene oxidation.

NO reduction by CO over automotive exhaust gas catalysts in the presence of O2

The reduction of NO by CO in absence and presence of O2 has been investigated by transient experiments at automotive cold-start conditions over Pt/Rh/CeO2/γ-Al2O3, and derived model catalysts. A high-resolution magnetic sector mass spectrometer was used for distinguishing CO/N2 and CO2/N2O. Mechanistic comparisons are made between the catalyst formulations. A kinetic scheme of elementary reaction steps is proposed, which highlights the various contributions of the catalyst constituents.

Coke Deposition on Automotive Three-Way Catalysts Studied with LEIS

LEIS measurements have been performed on fresh and used commercial three-way catalysts (Pt/Rh/CeO2/γ-Al2O3). The catalysts showed a significant decrease in the platinum surface concentration of approximately 50% after use in hydrocarbon oxidation at cold-start conditions, and could be completely regenerated. The selectivity towards the outermost atomic layer of LEIS allowed a one to one correlation between the surface Pt concentration as detected with LEIS and that obtained by kinetic modelling. This supports recent assumptions on selective deactivation. Conventional surface science techniques such as XPS, SIMS or AES would have yielded ambiguous results since their probing depths are not limited to the outermost atomic layer.

Automotive Exhaust Gas Conversion: From Elementary Step Kinetics to Prediction of Emission Dynamics

Elementary step based kinetics show a high added value to describe the performance of catalytic exhaust gas converters under dynamic conditions, as demonstrated with a Euro test cycle. Combination of such kinetic models for individual global reactions covers the mutual interactions via common adsorbates. Feed composition modulation as a transient kinetic technique provides detailed information about elementary steps and their rate parameters.

Kinetic modelling of transient NO reduction by CO in the presence of O2 over an automotive exhaust gas catalyst.

Abstract Kinetic rate coefficients have been determined for the reduction of NO by CO in absence and presence of O 2 via regression of transient experiments at automotive cold-start conditions over a commercial Pt/Rh/CeO 2 /γ-Al 2 O 3 catalyst. The kinetic model quantifies storage and release of O 2 and NO in ceria during lean and rich half-cycles.

Kinetics of the steady state acetylene oxidation by oxygen over a Pt/Rh/CeO2/gamma-Al2O3 three-way catalyst

The steady-state kinetics of acetylene oxidation has been studied in the framework of automotive exhaust gas catalysis over a commercially available three-way catalyst. Experiments under cold-start conditions have been carried out in a laboratory fixed-bed reactor, which can adequately be described by the developed elementary step model and rate parameters.

Transient kinetics of ethylene and carbon monoxide oxidation for automotive exhaust gas catalysis: experiments and modelling

Abstract The transient oxidation of ethylene by oxygen over a commercially available Pt/Rh/CeO 2 /γ-Al 2 O 3 three-way catalyst is described. Experiments were carried out in a fixed-bed micro reactor with two separate inlets, enabling alternate feeding of ethylene and oxygen. The experimental conditions were chosen as to obtain intrinsic kinetics, i.e. in the absence of external and internal mass and heat transport limitations. Also, these conditions resemble the cold-start period of an Otto engine in a car. For these conditions, only total oxidation of ethylene to carbon dioxide and steam was observed. From the shape of the CO 2 peaks, two types of adsorbed ethylene species seem to exist. The presence of ceria in the catalyst did not influence the ethylene oxidation significantly at the investigated conditions. A kinetic model, based on elementary reaction steps, is presented, which can be combined with the model for transient carbon monoxide oxidation on the same catalyst [ 1 ].