Angewandte Chemie International Edition
Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
For full article and contact information, see Angew. Chem. Int. Ed. 2001, 40 (6), 1061-1063
Reining in Energy Guzzlers
An ammonia catalyst
for the next generation?
Ammonia is of central importance to chemical industry and to society as a whole. It is the starting point for the generation of such diverse products as fertilizers, man-made fibers, dyes, and even pharmaceuticals, to name a few. However, the synthesis of ammonia from nitrogen and hydrogen takes a lot of energy: all together, ammonia production facilities consume about 1% of the world’s energy production! This makes ammonia production one of the largest energy consumers in the world. Research into improving this production process is thus correspondingly intensive. In Bochum, a team of chemists working with Martin Muhler is at the forefront of the battle - and reports an important step forward: a new catalyst that could make the formation of ammonia more efficient.
All current ammonia production facilities are based on a synthetic process - awarded the Nobel Prize in 1919 - developed by Fritz Haber. In the hands of Carl Bosch, it was then further developed to a large-scale industrial process, for which he was given a Nobel Prize in 1931.
A large factory can produce 1,500 tons of ammonia daily. At the heart of the Haber-Bosch process are large, cylindrical catalytic reactors, often over 20 meters high, in which nitrogen and hydrogen react over about 100 tons of an iron catalyst. Harsh conditions reign within the cylinders: high pressures in the 200 to 500 bar range and high temperatures between 400 and 600 °C are necessary to obtain sufficiently high yields of ammonia in a short time. It is mainly the generation of the high pressure that consumes enormous amounts of energy. A more efficient catalyst, one that works at a lower pressure, could remedy the situation.
Muhler and his coworkers bet on ruthenium as a catalyst component. They developed a new preparation technique that allowed them to apply the ruthenium onto a magnesium oxide support. However, the catalyst only gets its extra kick once barium compounds, which act as activators, are added. This new catalyst is substantially more effective than all previously described catalyst systems. In comparison with conventional iron catalysts, the new ruthenium catalyst delivers significantly higher yields. Or, to put it another way: in order to get similar yields, the iron requires twice the pressure required by the new ruthenium system. "Our new catalyst will be the ammonia catalyst of the next generation," Muhler is convinced.