He retired a broken man, although at the time of his death he was on his way to investigate a possible senior research position in Rehovot in Palestine now Israel. On May 1, , Clara Immerwahr Haber sat down at her desk to write farewell letters to friends and family. Part 3 of Our Chemical Landscape. This episode: how crop production has evolved in response to exploding global population growth. What happened before humans could produce fertilizer from the air itself, courtesy of the Haber-Bosch process?
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Updated April 10, Featured Video. Cite this Article Format. Briney, Amanda. Overview of the Haber-Bosch Process. An Introduction to Male and Female Gonads. Overview of the Second Industrial Revolution. When nitrogen compounds run off into rivers, they likewise promote the growth of some organisms more than others. The results include ocean "dead zones", where blooms of algae near the surface block out sunlight and kill the fish below. The Haber-Bosch process is not the only cause of these problems, but it is a major one, and it is not going away.
Demand for fertiliser is projected to double in the coming century. In truth, scientists still do not fully understand the long-term impact on the environment of converting so much stable, inert nitrogen from the air into various other, highly reactive chemical compounds.
One result is already clear: plenty of food for lots more people. If you look at a graph of global population, you will see it shoot upwards just as Haber-Bosch fertilisers start being widely applied.
Again, Haber-Bosch was not the only reason for the spike in food yields. New varieties of crops like wheat and rice also played their part. Still, if we farmed with the best techniques available in Fritz Haber's time, the earth would support about four billion people.
Our current population is around seven and a half billion, and growing. Back in , as Haber triumphantly demonstrated his ammonia process, he could hardly have imagined how transformative his work would be. On one side of the ledger, food to feed billions more human souls; on the other, a sustainability crisis that will need more genius to solve.
For Haber himself, the consequences of his work were not what he expected. As a young man, he converted from Judaism to Christianity, aching to be accepted as a German patriot. When the Nazis took power in the s, however, none of this outweighed his Jewish roots.
Stripped of his job and kicked out of the country, Haber died, in a Swiss hotel, a broken man. In the future, will farming be fully automated? Prince of Wales joins soil boosting project. Ammonia synthesis at a wind farm could help solve one of the biggest problems with renewable energy sources—they produce energy intermittently.
Burning ammonia produced renewably may be one answer, Wilkinson says. Both Siemens and JGC are interested in green ammonia production not just to make fertilizer but also to synthesize a carbon-free fuel. Similar to gasoline, ammonia can be shipped and stored, and it is easier to deal with than gaseous hydrogen, another possible carbon-free fuel.
And companies already ship ammonia across oceans for current uses, MacFarlane says. Related: Making ammonia with water and nitrogen.
The reaction involves combining hydrogen and nitrogen gas over an iron catalyst, at high temperatures and pressures. Each metric ton of ammonia packs about 5 MW h of energy. Switching to renewable feedstocks and energy sources is a good solution in the short term, Manthiram says, because companies can effectively combine current renewable energy technologies with Haber-Bosch. But to improve the sustainability of ammonia synthesis over the long term, scientists have to change the game entirely.
Research in the field has taken off since about , perhaps because of expanded funding availability as federal agencies have started to focus on the topic, says Lauren Greenlee, a chemical engineer at the University of Arkansas. Researchers are trying a wide range of approaches: electrochemistry, electrocatalysis, photocatalysis , and photoelectrocatalysis.
Electrochemical reduction of nitrogen to ammonia over a catalyst has captured the imagination of many scientists. The chemists apply a voltage across an electrochemical cell to drive both water oxidation and nitrogen reduction simultaneously. The catalyst at the anode oxidizes water to form hydrogen ions, which migrate to the cathode, where a different catalyst reduces nitrogen to ammonia. Scientists have developed numerous electrochemical ammonia-synthesis catalysts, including noble-metal nanostructures, metal oxides, metal nitrides, metal sulfides, nitrogen- and boron-doped carbon, and lithium metal.
Electrochemistry also presents a good way to solve a trade-off between reaction rates and yields that chemists must face when running the Haber-Bosch reaction, Manthiram says. The reaction has good yields at very low temperatures, he says, but the rate is sluggish. To speed it up, chemists raise the temperature. So chemists raise the pressure to bring the yields back up.
One of the other possible advantages of the electrochemical approach is that the reaction system can be small. Meanwhile, other researchers are looking to nature to understand how to efficiently reduce nitrogen to ammonia. Some bacteria use large protein complexes called nitrogenases to grab nitrogen out of the air and make ammonia. Minteer and her team have been studying this system to connect these bacterial enzymes to electrodes to create new electrocatalysts.
But they still have a long way to go, Minteer says. Their systems do more proton reduction than ammonia production. Scientists throughout the field face this problem with catalyst yield and selectivity.
As a result, the ammonia coming out of these non-Haber-Bosch systems is a trickle, not a torrent. Once the bond breaks, the catalyst needs to form the three nitrogen-hydrogen bonds, all at ambient conditions without high temperatures to accelerate the kinetics. Scientists have been intensely studying hydrogen-evolution catalysts for about the past 20 years. Greenlee points out that the solutions have to go beyond catalyst design. Scientists need to figure out how to control, reduce, or eliminate the hydrogen-evolution reaction.
For a new ammonia production system to be practical, such as in an electrochemical device like the one his group is working on, catalysts will need to remain active and viable for years, even if the system could be taken apart and refurbished, he says.
Related: Tackling sustainable fertilizer production with an alternative electrolyte. The road to Haber-Bosch-free ammonia is long, Minteer says. Searching for alternatives to Haber-Bosch is also risky, Manthiram says, because what scientists are pursuing now may not pan out. But with ammonia production touching so many things that we use every day, including our food and pharmaceuticals, scientists need to find a way to make these lab-scale systems work on larger scales, he says.
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