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The temperature programmed desorption (TPD) is used to determine the experimental conditions needed to characterize the dispersion of precious metals by hydrogen chemisorption on three way exhaust gas catalysts. It is shown that hydrogen chemisorption on the samples is activated. An adsorption temperature of 370-473 K must be used in order to obtain a fast saturation of the sites. In these conditions, the support of the precious metals chemisorbs H2 as well. Only the TPD method permits to distinguish the two sites of adsorption. For the various fresh industrial catalysts studied the metal dispersion is around 100 % using a ratio H/metal=1. The change of the hydrogen chemisorption with the thermal ageing of the catalysts under inert gas is studied.

A laboratory scale analytical procedure is described to determine the efficiency of three way exhaust gas catalysts (Pt/Rh/monolith) by F.T.I.R. spectroscopy. An extruded part of monolith was used to convert synthetic gas mixtures (CO/NO/Hydrocarbons/CO2/H2O/N2) which have compositions similar to motor vehicule exhaust gases. The catalyst efficiency was determined as a function of gas temperature and equivalent air-fuel ratio (with and without perturbation). F.T.I.R. spectroscopy appears as an alternative method compared to the present one using several specific detectors. Comparative data are obtained on the conversion of CO, NO and hydrocarbons. In addition F.T.I.R. spectroscopy was capable of giving the following informations: the conversion of each hydrocarbons (in case of mixture of hydrocarbons), the transient formation of N2O and the occurence of NO2.