CATALYTIC CONTROL OF DIESEL-ENGINE PARTICULATE EMISSION - STUDIES ON MODEL REACTIONS OVER A EUROPT-1 (PT SIO2) CATALYST/

The catalytic oxidation of nitric oxide to nitrogen dioxide in the pre sence of sulphur dioxide over a standard Pt/SiO2 Catalyst (EuroPt-1) w as studied. The gas-phase reactions between nitric oxide, sulphur diox ide and oxygen were found to be insignificant under the experimental c onditions concerned. The Pt/SiO2 catalyst was observed to be very acti ve in catalyzing the reactions both of NO + O2 to NO2 and of SO2 + O2 to SO3. In the presence of sulphur dioxide, the catalytic activity for nitric oxide oxidation dropped dramatically, and in contrast, the pre sence of nitric oxide promoted sulphur dioxide oxidation. There ia sig nificant influence of NO/NO2 on sulphur dioxide oxidation; there are i ndications from temperature-programmed desorption and temperature-prog rammed reduction (TPR) that some sort of complex species (e.g. [N(x)-S (y)-O(z)]) is formed on the platinum surface. Deactivation of the cata lyst was also observed during the activity tests. It is believed that the deactivation of the catalyst was mainly caused by the build-up of some nitrogen and sulphur compounds on the active sites of the platinu m catalyst. Another reason for the deactivation could be the sintering of platinum particles in the reaction environment. This has been conf irmed by X-ray photoelectron spectroscopy, TPR and platinum dispersion measurements.