TY - GEN
T1 - Studies to the functioning of automotive exhaust catalysts using in-situ positron emission tomography
AU - Vonkeman, K.A.
AU - Jonkers, G.
AU - Santen, van, R.A.
PY - 1991
Y1 - 1991
N2 - Studying the reactions in an automotive exhaust catalyst is complex as the exhaust gases contain many components of which the composition constantly varies and the catalyst contains different active components. To elucidate reaction kinetics in exhaust catalysis, the application of a technique stemming from nuclear medicine, i.e. Positron Emission Tomography, has been developed. Short lived positron emitting nuclides 11C (t1/2 = 20 min), 13N (t1/2 = 10 min) and 15O (t1/2 = 2 min) have been used to synthesize actual reactant molecules such as 11CO, 11CO2, 11CH4, 13N2, 15OO, C15O and C15OO. Pulses of picomole amounts of these labelled reactants have been added to synthetic exhaust gases, which were led over commercial and model automotive catalysts in a small plug flow reactor. The labelled compounds were detected and identified in both reactant and product stream using a gas chromatograph equipped with a proportional counter. On top of that, the labelled reactants in the catalyst bed could be monitored right through the reactor wall using a Positron Emission Tomograph, with a resolution of 1 cm in place and 1 s in time. Hereby, a large amount of information on the residence time of the reactants is obtained directly from the catalyst surface under actual reaction conditions. By means of these experiments the rate limiting step in the carbon monoxide oxidation on platinum and rhodium under cold start conditions of a car were found to be the availability of free noble metal surface for the dissociative oxygen adsorption. The different behaviour of rhodium and platinum in the CO oxidation in the presence of NO was found to be the higher tendency for NO dissociation of rhodium. A strong interaction was found between gas phase CO2 and CeO2 at the catalyst surface, whereby the oxygen atoms contained in lattice CeO2 exchange rapidly with the oxygen atoms of the adsorbed CO2. A mathematical model for the reaction kinetics was constructed and by simulating the experiments with this model the kinetic parameters were quantified. The experiments demonstrate the utility of short-lived positron emitter nuclides such as 11C, 13N and 15O, for non-invasive and in-situ catalyst research. The importance of using in-situ catalyst surface information in understanding the working of automotive exhaust catalysts under actual reaction conditions is emphasized. [Author abstract; 43 Refs; In English]
AB - Studying the reactions in an automotive exhaust catalyst is complex as the exhaust gases contain many components of which the composition constantly varies and the catalyst contains different active components. To elucidate reaction kinetics in exhaust catalysis, the application of a technique stemming from nuclear medicine, i.e. Positron Emission Tomography, has been developed. Short lived positron emitting nuclides 11C (t1/2 = 20 min), 13N (t1/2 = 10 min) and 15O (t1/2 = 2 min) have been used to synthesize actual reactant molecules such as 11CO, 11CO2, 11CH4, 13N2, 15OO, C15O and C15OO. Pulses of picomole amounts of these labelled reactants have been added to synthetic exhaust gases, which were led over commercial and model automotive catalysts in a small plug flow reactor. The labelled compounds were detected and identified in both reactant and product stream using a gas chromatograph equipped with a proportional counter. On top of that, the labelled reactants in the catalyst bed could be monitored right through the reactor wall using a Positron Emission Tomograph, with a resolution of 1 cm in place and 1 s in time. Hereby, a large amount of information on the residence time of the reactants is obtained directly from the catalyst surface under actual reaction conditions. By means of these experiments the rate limiting step in the carbon monoxide oxidation on platinum and rhodium under cold start conditions of a car were found to be the availability of free noble metal surface for the dissociative oxygen adsorption. The different behaviour of rhodium and platinum in the CO oxidation in the presence of NO was found to be the higher tendency for NO dissociation of rhodium. A strong interaction was found between gas phase CO2 and CeO2 at the catalyst surface, whereby the oxygen atoms contained in lattice CeO2 exchange rapidly with the oxygen atoms of the adsorbed CO2. A mathematical model for the reaction kinetics was constructed and by simulating the experiments with this model the kinetic parameters were quantified. The experiments demonstrate the utility of short-lived positron emitter nuclides such as 11C, 13N and 15O, for non-invasive and in-situ catalyst research. The importance of using in-situ catalyst surface information in understanding the working of automotive exhaust catalysts under actual reaction conditions is emphasized. [Author abstract; 43 Refs; In English]
U2 - 10.4271/910843
DO - 10.4271/910843
M3 - Conference contribution
T3 - SAE (Society of Automotive Engineers) Transactions
SP - 371
EP - 385
BT - SAE (Society of Automotive Engineers) Transactions
PB - Society of Automotive Engineers (SAE)
CY - Detroit
T2 - 1991 SAE International Congress and Exposition
Y2 - 25 February 1991 through 1 March 1991
ER -