In order for the converter to operate properly, several conditions must be met. First, the exhaust gasses must be at or above a certain temperature. This is why the converter is placed close to the engine. Second, there must be a certain minimum surface area of catalyst for the gasses to come in contact with. This is the reason for the honeycomb design. It provides a large surface area in a small space. Third, the ratio of exhaust gas to air must be maintained within very rigid limits. If these limits are not observed, the converter will not function and could even be damaged. These limits are maintained by placing a oxygen sensor in the exhaust just before the converter.
