The catalytic converter is a marvel of chemical and technological engineering. It cleans gases passing through vehicles’ exhaust systems. Catalytic converters typically consist of a ceramic or metal honeycombed monolith substrate that carries precious metal catalysts. The coated substrate is wrapped in a protective thermal mat that expands when heated, securing and insulating the substrate, which is contained in a tough stainless steel shell and becomes a component in an engine exhaust system. As exhaust gases pass over the catalysts, chemical reactions occur that convert pollutants into harmless gases and water. Hydrocarbons combine with oxygen to become carbon dioxide. Nitrous oxides react with carbon monoxide to produce nitrogen and carbon dioxide, and with hydrogen to produce nitrogen and water vapor.