Catalytic Converter

Palmer's Auto Repair - Catalytic Converter | imagePalmer's Auto Repair can diagnose catalytic converter problems and replace catalytic converters. Just a few of the problems you can experience are: one of the catalyst plates gets loose and rattles; the converter gets clogged and causes the car to run rough and get terrible gas mileage; they can leak exhaust;  they can wear out and stop doing their job.

Catalytic converters have no moving parts but they do have a number of features that can cause major problems with your vehicle.   Here's an explanation how a catalytic converter works.

Newer cars control the amount of fuel they burn electronically so that there is very little left over once the fuel and air are burned by the engine. Theoretically, all of the fuel gets burned and all of the oxygen gets burned. Unfortunately, the fuel mixture varies quite a bit during driving and it isn't always perfect so you end up with emissions.

The by-products (emissions) when you run a gasoline engine are Nitrogen gas (N2), Carbon dioxide (CO2), and water (H2O).  These gases are mostly benign and don't require emission control.

Because the combustion process is never perfect, some small amounts of harmful emissions are also produced by car engines: Carbon monoxide (CO), Hydrocarbons (VOCs), and Nitrogen oxides (NO NO2, and NOx). These three gases contribute to smog and acid rain, and are irritants to your eyes, nose, and throat. Catalytic converters are designed to reduce these harmful emissions.  They do this by using catalysts.

A catalytic converter uses two different types of catalysts.  They use a reduction catalyst and an oxidation catalyst. Both types consist of a ceramic structure coated with a metal catalyst,: platinum, rhodium and/or palladium. The unit is designed so that the exhaust flows over the catalyst surface on its way through the exhaust stream.  Most modern cars are equipped with three-way catalytic converters. This refers to the three regulated emission gases that are reduced by the two catalysts.

A reduction catalyst is the first stage of a catalytic converter. It uses platinum and rhodium to reduce the NOx emissions. When an NO or NO2 molecule contacts the catalyst, the catalyst breaks the molecule.  The nitrogen atom pops out of the molecule and sticks to the catalyst, freeing the oxygen. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2.

The oxidation catalyst is the second stage of a catalytic converter. It reduces unburned hydrocarbons and carbon monoxide by burning (oxidizing) emissions over a platinum / palladium catalyst. This catalyst aids the reaction of the CO and hydrocarbons using the remaining oxygen in the exhaust. Just so you know, every one of these catalyst materials is more expensive than gold.  That's why a quality replacement converter is expensive.

Palmer's Auto Repair - O2 Sensor | imageLastly, there is an exhaust system monitoring system that senses how much CO, VOC, and NOx there is in the exhaust. These monitors control the fuel/air mixture at the engine intake. In particular, an oxygen sensor is mounted in the exhaust before the catalytic converter. It tells the engine computer how much oxygen is in the exhaust. The monitor will increase or decrease the amount of oxygen in the exhaust by adjusting the air-to-fuel ratio. This allows the engine to run at its highest efficiency and makes sure that the catalytic converter is eliminating the maximum amount of unwanted emissions.