Carl Keith was a research chemist who invented, with his colleague John J. Mooney, the three-way catalytic converter. This device has been responsible for the large reduction of atmospheric pollution since the mid-1970s when it was incorporated into motor vehicles of all kinds as well as static machines with engines, such as generators.

A catalytic converter, often known as a “cat” or “catcon”, reduces the toxicity of emissions from the exhaust of an internal combustion engine. In it a chemical reaction converts toxic combustion by-products — chiefly nitrogen oxides, carbon monoxide and hydrocarbons — into substances that are less toxic.

The three-way catcon performs three tasks simultaneously. It converts nitrogen oxides to nitrogen and oxygen, oxidises carbon monoxide to carbon dioxide, and oxidises unburnt hydrocarbons to carbon dioxide and water.

Before Keith and Mooney developed the three-way catcon, the available converters were oxidation catalysts, which could deal with hydrocarbons and carbon monoxide but not with nitrogen oxides. The car manufacturers badly needed a device that would deal with all three exhaust pollutants in a single process. The 1970 amendments to the US Clean Air Act, for example, required significant reductions in hydrocarbon, carbon monoxide and nitrogen oxide emissions. Keith and Mooney’s catcon achieved this using a single catalyst bed.

Inside the catcon a ceramic honeycomb, with a large number of tiny passages, is coated with the catalytic material, typically platinum and rhodium or palladium. When the engine exhaust passes over and through the catalyst coating, a chemical reaction renders the nitrogen oxides, carbon monoxide and unburnt hydrocarbons harmless.

The three-way catcons developed by Keith have been installed in cars since 1975 and are used today in some 80 per cent of the new cars manufactured worldwide. It has been calculated that they have prevented more than 70 million tons of hydrocarbons, 150 million tons of nitrogen oxides and 600 billion tons of carbon monoxide being emitted into the atmosphere.

The invention of the catcon has dramatically improved the quality of the air we breathe and enabled the car industry to meet clean-air regulations. It has also helped to eliminate lead, a pollutant known to damage the mental health of children, from the atmosphere. It is no exaggeration to say that catcon has saved hundreds of thousands of lives and prevented the occurrence of several respiratory diseases.

Ironically, because they are installed on the outside of a vehicle and because they incorporate precious metals, including platinum, palladium, and rhodium, catcons are also an attraction to thieves.

Carl Donald Keith was born in 1920 in Stewart Creek, West Virginia, one of three sons of Howard and Mary Rawson Keith. His father was a steelworker, and his mother worked in a bakery. He studied at Salem College, in Winston-Salem, North Carolina, receiving his bachelor’s degree in 1943. He then moved to Indiana University, where he was awarded a master’s degree in chemistry in 1945. He received his doctorate from DePaul University, Chicago, in 1947.

In 1943 he had begun his career as a research chemist at Sinclair Oil in Salt Lake City, where he worked until 1957. He then joined Engelhard Corporation, in New Jersey, one of the world’s largest mineral refining companies. He stayed with the company until he retired in 1985. He served as an executive vice-president, president and then chairman of the company. He received more than 200 patents.

In 2003 President George W. Bush presented Keith and Mooney with the US National Medal of Technology and Innovation, the US’s highest honour for technological innovation, for their invention of the catcon and its commercialisation.

Keith received numerous other awards, including the Walter Ahlstrom Prize, which is awarded for engineering achievements that have led to important benefits in industry and to the well-being of society.

His wife died in 2000, and two daughters survive him.

Carl Keith, research chemist, was born on May 29, 1920. He died on November 9, 2008, aged 88