Fritz Haber made ammonia from the air in 1909

Person: Fritz Haber
Lived: 1868–1934
Field: Chemistry
From: German

The story

Nitrogen makes up most of the air, but plants cannot use it in that form. At the start of the twentieth century farmers depended on limited natural sources of fixed nitrogen, chiefly nitrate mined in Chile and guano from tropical islands, and these were expected to run short. Turning atmospheric nitrogen into a usable compound was a long-sought goal that no one had achieved on a practical scale, because nitrogen gas is so unreactive.

Fritz Haber, born in 1868 into a Jewish family in Breslau, was then professor of physical chemistry and electrochemistry at Karlsruhe. In his 1905 book on the thermodynamics of technical gas reactions he had already recorded small amounts of ammonia formed from nitrogen and hydrogen with an iron catalyst at 1,000 °C. The yield was tiny. Chemists understood from Le Châtelier's principle that high pressure would push the reaction towards ammonia, and that lower temperatures favoured it too, but made it far too slow without a good catalyst.

With his assistant Robert Le Rossignol, a young British chemist from Jersey, he built high-pressure apparatus and searched for better catalysts and conditions. In the summer of 1909 they succeeded by circulating nitrogen and hydrogen over a catalyst at about 500 °C and a pressure of 150 to 200 atmospheres. Their tabletop machine produced ammonia drop by drop, about 125 millilitres an hour. Le Rossignol's name appears on Haber's patents for the process.

The chemical company BASF bought the process, and its engineer Carl Bosch, with the chemist Alwin Mittasch, scaled it up. Industrial production began in 1913 at Oppau. The method became known as the Haber–Bosch process.

Haber was awarded the 1918 Nobel Prize in Chemistry for the synthesis of ammonia from its elements. In his Nobel lecture he acknowledged that nitrogen-fixing bacteria still used natural methods that chemists did not yet know how to imitate. More than a century later, ammonia made by his method underpins the fertiliser that grows a large share of the world's food.

Why it matters

Haber's laboratory synthesis opened the way to making nitrogen fertiliser from the air, one of the most consequential chemical advances in history.

About Fritz Haber

Nobel chemist whose ammonia synthesis made the fertilisers that feed billions, who also led Germany’s WWI poison-gas programme, and who was driven out by the Nazis.

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Fritz Haber

1868–1934 · Chemistry

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