PERFORMANCE OF THE AUTOMOTIVE 3-WAY CATALYTIC-CONVERTER

A three-way catalyst is a multifunctional supported catalyst which is capable of converting the major automotive pollutants: CO, HC's, and N O,, simultaneously. Three-way catalyst systems have been developed as a result of the strict automotive emission regulations (especially for NOx) which came into force in the USA in 1981. Gas concentration and temperature play an important role in the efficiency of three-way cata lysts for the removal of CO and HC's from automotive exhaust gas. One of the methods used for evaluating the performance of the three way ca talyst is to change the feed gas temperature and measure the correspon ding conversions at various oxygen concentrations. Recent studies have reported the effect of oxygen concentration and temperature on the co nversion of propane and n-hexane in a model gas test over the three wa y catalyst. In this paper, the performance of the three way catalyst u nder realistic engine conditions was studied. A prototype 4-stroke one cylinder stationary internal combustion engine was utilized as a sour ce of exhaust gas. The effect of oxygen concentration and temperature were traced. The three-way catalyst efficiency appeared to be strongly dependent on the oxygen partial pressure. The three-way catalyst perf ormance is generally enhanced with increase in oxygen concentration. T he three-way catalyst was found to be more active for conversion of CO than for HC's. Under reducing conditions, the conversion curves for C O and HC's were observed to go through a maximum and then decline shar ply with temperature. These declines started at a temperature of about 286 degrees C. This inhibition might be ascribed to chemisorption of CO, NO, and HC's on the catalyst active sites and to the consumption o f oxygen in undesired reactions such as hydrogen oxidation.