Since I'm a chemist, I guess I should jump in on this. There are 2 catalysts inside the cat. The first are platinum-rhenium alloys, which are used to interconvert the hydrocarbons entering the cat. The second catalysts are platinum-rhodium alloys, which help the CO, O2, and the interconverted hydrocarbons to oxidize to CO2. The platinum-rhodium catalysts also reduce NOx to N2. Craig '92 100S (78k)