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30 Undercar Digest What Is Really Going on in that Catalyst? By Ed Hanson K nowledge is power. So the more we know about exhaust and emission-control products, the easier it is to explain how they work and why they fail. When I saw my very first cata- lyst in 1975, I believed that the honeycomb substrate was working all the magic, but after a few semi- nars I realized that there was a lot going on in that catalyst. The actual catalyst is a sub- stance or substances that cause the chemical reaction. In our case, most catalyst manufacturers use a CorningWare or similar substrate (Figure 1) as the platform to apply their catalyst. The substrate is held in place by a vermiculite blanket, which keeps the "brick" or sub- strate from bouncing around in the stainless steel shell and breaking apart. Most manufacturers use platinum, palladium, rhodium and an element called cerium for their reactants. There is less than 1 /4 ounce of precious metal load in the entire catalyst to do the reduction and oxidation. From the beginning, when we burn our fossil fuels (our gasoline), there are some byproducts that are harmful to us. Such as hydrocar- bons, carbon monoxide and oxides of nitrogen (NOx). After our pre- liminary emissions-control devices have done their job, what is left must be handled by our catalytic converters. To start the process off, we have the reduction portion of our catalyst. Most manufacturers use rhodium and cerium for the re- duction part of the catalyst. The rhodium strips the oxygen from the NOx and stores the oxygen in the cerium. During the rich cycle of the oxygen sensor, the cerium releases the oxygen molecules and the oxidation process begins. Now the platinum and palladium get to work changing the hydrocarbons into water and the carbon monox- ide into carbon dioxide. None of this process can occur if the light-off temperature of 400- 800° F has not been reached along Illustrations courtesy of Eastern Catalytic The Best Choice – ADVICS Disc Brakes and Ultra-Premium Brake Pads The optimum control derived from ADVICS brake products assures safe and reliable vehicle performance for passenger cars and light trucks. Rotor wear can be attributed to many reasons, including the type of brake pad chosen. When replacing rotors with ADVICS Disc Brakes, it's a good idea to also replace the brake pads with ADVICS Ultra-Premium Brake Pads. • OE precision fit for safe, consistent braking performance • Exacting tolerances ensure immediate and reliable response to pedal input • Free flowing air through brake discs provides even heat dissipation for longer life • Brake pads engineered to virtually eliminate vibration, noise and pedal shudders As a premier supplier of original- equipment brake system products to well-known manufacturers such as Toyota and Lexus, ADVICS manufac- tures superior-quality, performance- driven braking components. These spec- ifications are derived from extensive testing and engineering, including vehi- cle movement simulations, brake squeal and vibration analysis, dynamometer performance testing, durability assess- ment, and in-vehicle calibration studies. Contact ADVICS today at amsales@advics-na.com Circle No. 33 on Reader Card