High-pressure chemistry is a technique that applies hundreds of atmospheres of pressure to alter molecular motion, controlling reaction rates and products. Bosch and Bergius created robust steel pressure vessels and efficient catalysts, completing the industrial scale-up of the Haber–Bosch process, which converts nitrogen and hydrogen into ammonia. Ammonia is the precursor of nitric acid and urea and, as a fertilizer, dramatically boosted agricultural yields, easing world hunger. Bergius also invented a hydrogenation process that turns coal into liquid fuels, opening the path to synthetic gasoline. Their achievements underpin efficient use of resources and the large-scale growth of the chemical industry.

At the beginning of the 20th century, Fritz Haber had demonstrated catalytic nitrogen fixation in the laboratory, but practical exploitation required reactors that could survive about 500 bar and roughly 700 K. Carl Bosch engineered thick-walled reactors made from high-manganese and Cr-Mo steels, overcoming leakage, stress corrosion, and cyclic fatigue. He simultaneously optimized the Fe–K2O–Al2O3 catalyst system, greatly improving equilibrium yields and catalyst longevity. Friedrich Bergius, in parallel, developed a coal-hydrogenation liquefaction process—the Bergius process—in which coal dust suspended in heavy oil is hydrogenated under high pressure, cleaving hydrocarbon chains and yielding lighter oils. Both high-pressure technologies manipulated thermodynamic equilibria and reaction kinetics to convert air or coal into high-value chemicals, creating an industrial paradigm still relevant to modern petroleum refining and emerging green-ammonia research.

Bosch adopted multilayer cylinders with shrink-fitted prestressed shells, scaling nitrogen-fixation reactors from the 20 MPa laboratory scale to over 50 MPa industrial units. To suppress iron nitride formation, partially reduced Fe3O4 promoted with K2CO3/Al2O3 was employed as the catalyst precursor, yielding highly active α-Fe under reaction conditions. In the Bergius process, aromatic frameworks in coal are hydrogenated at 420 °C and 30 MPa over MoS2-based catalysts, inducing reductive C–C scission and converting heavy asphaltenes to C5–C10 fractions. Process design incorporated mixing control via Bodenstein numbers, equilibrium displacement guided by Le Châtelier’s principle, and high-pressure phase behavior modeled with Peng–Robinson EOS, thereby foreshadowing modern chemical-engineering methodology. Even today, urea plants and slurry-loop Fischer–Tropsch reactors reference these high-pressure design principles as benchmarks.