PREPARATION, ACTIVITY AND DURABILITY OF PROMOTED PLATINUM CATALYSTS FOR AUTOMOTIVE EXHAUST CONTROL

The effects of the addition of calcia, ceria and lanthana to alumina-s upported platinum catalysts on the simultaneous control of hydrocarbon , carbon monoxide and nitrogen oxide automobile emissions (three-way c atalyst behaviour) were analyzed. The activity of the prepared samples was determined with steady-state, reducing and oxidizing, simulated f eedstreams as well as with a cycled oxidizing-reducing feedstream aver aged at the stoichiometric conditions which resembled the exhaust air/ fuel fluctuations in a closed-loop emission control system. Activity o f the catalysts was also analyzed after conducting accelerated thermal and chemical ageing in order to test their durability. Under normal o perating conditions of the automobile engine, Pt/Al2O3 catalysts promo ted by rare-earth oxides are able to achieve high HC, CO and NO conver sions. The behaviour of the catalysts in the cold start period was det ermined by analysis of light-off temperatures and a comparison was mad e with those corresponding to some commercial samples and others repor ted in the literature. The catalysts prepared in this work showed lowe r light-off temperatures than those of commercial and reported Pt/Al2O 3 catalysts but these temperatures were not so low as with Pt-Rh/Al2O3 . In all cases, the prepared catalysts resulted in a better resistance to accelerated ageing. Samples with ceria showed the best resistance to accelerated ageing.