Pioneering thinker - then and now:
His arrival in Ludwigshafen heralded the beginning of a truly remarkable career: Having just completed his doctorate in chemistry at the Frederick William University in Berlin (now Humboldt University), Carl Bosch joined BASF in 1899, where the 25-year-old was given a research task that would shape the rest of his life. His challenge was to find out how to synthetically combine nitrogen and hydrogen to create ammonia.
The big breakthrough came in 1913. Carl Bosch was able to take the ammonia synthesis process developed by Fritz Haber and move it from the laboratory to industrial-scale production. He thus made it possible to independently produce mineral fertilizers, of which ammonia is a basic ingredient. His achievement helped to feed millions of people worldwide. For this process, Bosch developed a new high-pressure technology using reliable plants with special reactors and new kinds of steel. Since then, the Haber-Bosch process has enabled large quantities of ammonia to be produced from atmospheric nitrogen and hydrogen – which today is mostly derived from natural gas – using an iron catalyst.
One hundred years ago, BASF built the world’s first industrial production plant for ammonia in Oppau, now part of Ludwigshafen, Germany. At the same time, Bosch was named an authorized signatory of the company – and became Chairman of the Board of Executive Directors just six years later. In 1925, he assumed the role of Chairman of the newly founded company I.G. Farben, a merger between BASF, Höchst, Bayer and other chemical companies. When Adolf Hitler seized power in Germany, Bosch was faced with a moral conflict. On the one hand, the business profited from the Nazis. On the other hand, Bosch – who had liberal leanings and vehemently rejected National Socialism – tried to persuade Hitler to save Jewish scientists from persecution, but was unsuccessful.
Bosch subsequently retreated more and more into his private life, without quite turning his back on the industry. He found refuge in the world of science. As a child, he had collected insects which he dissected or kept in heated terrariums he constructed himself. Over his lifetime, this collection grew to include millions of beetles, butterflies and minerals. Bosch even bought an additional house to store everything. To study the stars, he had two observatories built in his garden.
The Nobel Prize he was awarded in 1931 was surely the greatest recognition of his life’s work. But this passionate observer of nature would have certainly also appreciated another honor: In 1990, 50 years after his death, an asteroid – 7414 Bosch – was named after him.
As a 12-year-old, Gerhard Ertl discovered his passion for chemistry thanks to a book called Successful chemical experiments (“Chemische Experimente, die gelingen”). But his mother eventually put a stop to his experimentation because of the “strange noises and smells” coming from his bedroom, so Ertl turned his attention to physics and started building innocuous radios instead. His passion for these two branches of science would shape the rest of his life, eventually even winning him the Nobel Prize. The physics professor was informed on his 71st birthday that he had been awarded the 2007 Nobel Prize in Chemistry for his groundbreaking findings in the field of heterogeneous catalysis.
“I use the methods of physics to answer questions related to chemistry,” says Ertl, describing his way of working. He also followed this approach in his research on the mechanisms behind the famous process of ammonia synthesis. Although, thanks to Carl Bosch, it had been possible to manufacture ammonia on an industrial scale since 1913, one question remained: What exactly was happening in the reaction on the surface of the iron catalyst? Ertl was the first to discover the secret of the molecular reaction – a milestone in the field of modern surface chemistry, for which he was later awarded the Nobel Prize. “Bosch was the engineer who enabled the large-scale application and I followed up later with the fundamental research,” says Ertl. Semiconductor physics first helped him get started with the detailed study of surface processes.
As a student of physical chemistry, Ertl wrote his doctoral thesis on the solid-gas interface, already working towards what would become his main subject matter. He received a post-doc qualification (habilitation) at the age of 31 with his investigation of the structural problems of chemical reactions on a crystalline solid surface. His research made him one of the most important chemists of our time. Ertl’s choice of a topic was clever – and daring – because at the time almost nothing was known about these phase boundaries. “This proved to be a very fruitful subject for my entire life,” reflects the 78-year-old.
But life outside the laboratory has also always been a priority for the interdisciplinary researcher. Ertl’s family and music are important to him. As a student, the passionate pianist was able to support himself by playing music in a dance band. Today, the professor emeritus and former director of the Fritz Haber Institute of the Max Planck Society in Berlin spends one evening a week as a répétiteur for the Berlin Oratorio Choir. But chemistry also gives Ertl an opportunity for art appreciation: “To this day, I still find aesthetic pleasure in a nice formula or a beautiful microscopic pattern.”
The reactive partners in the Haber-Bosch process are hydrogen and nitrogen, both diatomic gases. In order to turn these into ammonia, the strong triple bond in the nitrogen molecule and the single bond in the hydrogen molecule both have to be broken. This requires a lot of energy – or a catalyst like iron, which lowers the amount of activation energy. But what happens on the surface of the iron? Professor Dr. Gerhard Ertl discovered that the splitting of the nitrogen is the decisive step. The nitrogen molecule (N2) interacts so strongly with the electrons on the metallic surface of the catalyst that the bond between the two atoms in the nitrogen molecule is weakened and eventually breaks. This leaves both nitrogen atoms with three free electrons, enabling each atom to bond to three hydrogen atoms. At the end of the reaction chain, this combination forms ammonia as the final product. Chemical reactions on catalytic surfaces such as this one play an important role in many industrial applications, from mineral fertilizers to exhaust gas scrubbing.