Are catalytic converters required on diesel cars?

Catalytic converters are required on all new diesel cars in the United States and most other developed countries. Diesel engines produce higher levels of nitrogen oxides and particulate matter than gasoline engines, and catalytic converters help to reduce these emissions. Catalytic converters work by converting harmful pollutants into less harmful substances. In diesel engines, catalytic converters typically use a combination of platinum, rhodium, and palladium to convert nitrogen oxides into nitrogen and oxygen, and to convert particulate matter into carbon dioxide and water vapor.